breaking changes to the way targets work in zig

 * CLI: `-target [name]` instead of `--target-*` args.
   This matches clang's API.
 * `builtin.Environ` renamed to `builtin.Abi`
   - likewise `builtin.environ` renamed to `builtin.abi`
 * stop hiding the concept of sub-arch. closes #1526
 * `zig targets` only shows available targets. closes #438
 * include all targets in readme, even those that don't
   print with `zig targets` but note they are Tier 4
 * refactor target.cpp and make the naming conventions
   more consistent
 * introduce the concept of a "default C ABI" for a given
   OS/Arch combo. As a rule of thumb, if the system compiler
   is clang or gcc then the default C ABI is the gnu ABI.

5 files changed, 50 insertions, 73 deletions

diff --git a/std/build.zig b/std/build.zig
index d88a9b3270..e90d827602 100644
--- a/std/build.zig
+++ b/std/build.zig
@@ -731,20 +731,40 @@ const Version = struct {
 const CrossTarget = struct {
     arch: builtin.Arch,
     os: builtin.Os,
-    environ: builtin.Environ,
+    abi: builtin.Abi,
 };
 
 pub const Target = union(enum) {
     Native: void,
     Cross: CrossTarget,
 
+    fn archSubArchName(arch: builtin.Arch) []const u8 {
+        return switch (arch) {
+            builtin.Arch.arm => |sub| @tagName(sub),
+            builtin.Arch.armeb => |sub| @tagName(sub),
+            builtin.Arch.thumb => |sub| @tagName(sub),
+            builtin.Arch.thumbeb => |sub| @tagName(sub),
+            builtin.Arch.aarch64 => |sub| @tagName(sub),
+            builtin.Arch.aarch64_be => |sub| @tagName(sub),
+            builtin.Arch.kalimba => |sub| @tagName(sub),
+            else => "",
+        };
+    }
+
+    pub fn subArchName(self: Target) []const u8 {
+        switch (self) {
+            Target.Native => return archSubArchName(builtin.arch),
+            Target.Cross => |cross| return archSubArchName(cross.arch),
+        }
+    }
+
     pub fn oFileExt(self: *const Target) []const u8 {
-        const environ = switch (self.*) {
-            Target.Native => builtin.environ,
-            Target.Cross => |t| t.environ,
+        const abi = switch (self.*) {
+            Target.Native => builtin.abi,
+            Target.Cross => |t| t.abi,
         };
-        return switch (environ) {
-            builtin.Environ.msvc => ".obj",
+        return switch (abi) {
+            builtin.Abi.msvc => ".obj",
             else => ".o",
         };
     }
@@ -978,12 +998,17 @@ pub const LibExeObjStep = struct {
         }
     }
 
-    pub fn setTarget(self: *LibExeObjStep, target_arch: builtin.Arch, target_os: builtin.Os, target_environ: builtin.Environ) void {
+    pub fn setTarget(
+        self: *LibExeObjStep,
+        target_arch: builtin.Arch,
+        target_os: builtin.Os,
+        target_abi: builtin.Abi,
+    ) void {
         self.target = Target{
             .Cross = CrossTarget{
                 .arch = target_arch,
                 .os = target_os,
-                .environ = target_environ,
+                .abi = target_abi,
             },
         };
         self.computeOutFileNames();
@@ -1296,14 +1321,16 @@ pub const LibExeObjStep = struct {
         switch (self.target) {
             Target.Native => {},
             Target.Cross => |cross_target| {
-                zig_args.append("--target-arch") catch unreachable;
-                zig_args.append(@tagName(cross_target.arch)) catch unreachable;
-
-                zig_args.append("--target-os") catch unreachable;
-                zig_args.append(@tagName(cross_target.os)) catch unreachable;
-
-                zig_args.append("--target-environ") catch unreachable;
-                zig_args.append(@tagName(cross_target.environ)) catch unreachable;
+                const triple = builder.fmt(
+                    "{}{}-{}-{}",
+                    @tagName(cross_target.arch),
+                    Target.archSubArchName(cross_target.arch),
+                    @tagName(cross_target.os),
+                    @tagName(cross_target.abi),
+                );
+
+                try zig_args.append("-target");
+                try zig_args.append(triple);
             },
         }
 
diff --git a/std/fmt/index.zig b/std/fmt/index.zig
index f006dfdbdc..4f864b3662 100644
--- a/std/fmt/index.zig
+++ b/std/fmt/index.zig
@@ -1118,7 +1118,7 @@ test "fmt.format" {
         const result = try bufPrint(buf1[0..], "f64: {}\n", math.nan_f64);
         testing.expect(mem.eql(u8, result, "f64: nan\n"));
     }
-    if (builtin.arch != builtin.Arch.armv8) {
+    if (builtin.arch != builtin.Arch.arm) {
         // negative nan is not defined by IEE 754,
         // and ARM thus normalizes it to positive nan
         var buf1: [32]u8 = undefined;
diff --git a/std/os/linux/index.zig b/std/os/linux/index.zig
index ec90755164..b78c1b3da5 100644
--- a/std/os/linux/index.zig
+++ b/std/os/linux/index.zig
@@ -6,7 +6,7 @@ const vdso = @import("vdso.zig");
 pub use switch (builtin.arch) {
     builtin.Arch.x86_64 => @import("x86_64.zig"),
     builtin.Arch.i386 => @import("i386.zig"),
-    builtin.Arch.aarch64v8 => @import("arm64.zig"),
+    builtin.Arch.aarch64 => @import("arm64.zig"),
     else => @compileError("unsupported arch"),
 };
 pub use @import("errno.zig");
diff --git a/std/special/bootstrap.zig b/std/special/bootstrap.zig
index 1192d7e46f..950fd5cbb9 100644
--- a/std/special/bootstrap.zig
+++ b/std/special/bootstrap.zig
@@ -31,7 +31,7 @@ nakedcc fn _start() noreturn {
                 : [argc] "=r" (-> [*]usize)
             );
         },
-        builtin.Arch.aarch64v8 => {
+        builtin.Arch.aarch64, builtin.Arch.aarch64_be => {
             argc_ptr = asm ("mov %[argc], sp"
                 : [argc] "=r" (-> [*]usize)
             );
diff --git a/std/special/compiler_rt/index.zig b/std/special/compiler_rt/index.zig
index 6715df1805..7657ce6118 100644
--- a/std/special/compiler_rt/index.zig
+++ b/std/special/compiler_rt/index.zig
@@ -184,60 +184,10 @@ const is_arm_64 = switch (builtin.arch) {
 };
 
 const is_arm_arch = switch (builtin.arch) {
-    builtin.Arch.armv8_3a,
-    builtin.Arch.armv8_2a,
-    builtin.Arch.armv8_1a,
-    builtin.Arch.armv8,
-    builtin.Arch.armv8r,
-    builtin.Arch.armv8m_baseline,
-    builtin.Arch.armv8m_mainline,
-    builtin.Arch.armv7,
-    builtin.Arch.armv7em,
-    builtin.Arch.armv7m,
-    builtin.Arch.armv7s,
-    builtin.Arch.armv7k,
-    builtin.Arch.armv7ve,
-    builtin.Arch.armv6,
-    builtin.Arch.armv6m,
-    builtin.Arch.armv6k,
-    builtin.Arch.armv6t2,
-    builtin.Arch.armv5,
-    builtin.Arch.armv5te,
-    builtin.Arch.armv4t,
-    builtin.Arch.armebv8_3a,
-    builtin.Arch.armebv8_2a,
-    builtin.Arch.armebv8_1a,
-    builtin.Arch.armebv8,
-    builtin.Arch.armebv8r,
-    builtin.Arch.armebv8m_baseline,
-    builtin.Arch.armebv8m_mainline,
-    builtin.Arch.armebv7,
-    builtin.Arch.armebv7em,
-    builtin.Arch.armebv7m,
-    builtin.Arch.armebv7s,
-    builtin.Arch.armebv7k,
-    builtin.Arch.armebv7ve,
-    builtin.Arch.armebv6,
-    builtin.Arch.armebv6m,
-    builtin.Arch.armebv6k,
-    builtin.Arch.armebv6t2,
-    builtin.Arch.armebv5,
-    builtin.Arch.armebv5te,
-    builtin.Arch.armebv4t,
-    builtin.Arch.aarch64v8_3a,
-    builtin.Arch.aarch64v8_2a,
-    builtin.Arch.aarch64v8_1a,
-    builtin.Arch.aarch64v8,
-    builtin.Arch.aarch64v8r,
-    builtin.Arch.aarch64v8m_baseline,
-    builtin.Arch.aarch64v8m_mainline,
-    builtin.Arch.aarch64_bev8_3a,
-    builtin.Arch.aarch64_bev8_2a,
-    builtin.Arch.aarch64_bev8_1a,
-    builtin.Arch.aarch64_bev8,
-    builtin.Arch.aarch64_bev8r,
-    builtin.Arch.aarch64_bev8m_baseline,
-    builtin.Arch.aarch64_bev8m_mainline,
+    builtin.Arch.arm,
+    builtin.Arch.armeb,
+    builtin.Arch.aarch64,
+    builtin.Arch.aarch64_be,
     builtin.Arch.thumb,
     builtin.Arch.thumbeb,
     => true,