Set macOS/iPhoneOS/tvOS/watchOS ABI to none (unspecified) by default

Prior to this change we would assume the ABI for Apple targets to
be GNU which could result in subtle errors in LLVM emitting calls
to non-existent system libc provided functions such as `_sincosf`
which is a GNU extension and as such is not provided by macOS for example.
This would result in linker errors where the linker would not be
able to find the said symbol in `libSystem.tbd`.

With this change, we now correctly identify macOS (and other Apple
platforms) as having ABI `unknown` which translates to unspecified
in LLVM under-the-hood:

```
// main.ll
target triple = "aarch64-unknown-macos-unknown"
```

Note however that we never suffix the target OS with target version
such as `macos11` or `macos12` which means we fail to instruct LLVM
of potential optimisations provided by the OS such as the availability
of function `___sincosf_stret`. I suggest we investigate that in a
follow-up commit.

4 files changed, 11 insertions, 11 deletions

diff --git a/src/Compilation.zig b/src/Compilation.zig
index 7ac1e49196..2c15cb95a3 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -4289,7 +4289,7 @@ fn getZigShippedLibCIncludeDirsDarwin(arena: Allocator, zig_lib_dir: []const u8,
 
     list[0] = try std.fmt.allocPrint(
         arena,
-        "{s}" ++ s ++ "libc" ++ s ++ "include" ++ s ++ "{s}-{s}-gnu",
+        "{s}" ++ s ++ "libc" ++ s ++ "include" ++ s ++ "{s}-{s}-none",
         .{ zig_lib_dir, arch_name, os_name },
     );
     list[1] = try std.fmt.allocPrint(
diff --git a/src/link/MachO/Dylib.zig b/src/link/MachO/Dylib.zig
index 57c8238827..b8b8f50e67 100644
--- a/src/link/MachO/Dylib.zig
+++ b/src/link/MachO/Dylib.zig
@@ -303,7 +303,7 @@ const TargetMatcher = struct {
         };
         const os = @tagName(target.os.tag);
         const abi: ?[]const u8 = switch (target.abi) {
-            .gnu => null,
+            .none => null,
             .simulator => "simulator",
             else => unreachable,
         };
diff --git a/src/stage1/target.cpp b/src/stage1/target.cpp
index da6565f0be..81377b5d49 100644
--- a/src/stage1/target.cpp
+++ b/src/stage1/target.cpp
@@ -971,11 +971,7 @@ ZigLLVM_EnvironmentType target_default_abi(ZigLLVM_ArchType arch, Os os) {
         case OsOther:
             return ZigLLVM_EABI;
         case OsOpenBSD:
-        case OsMacOSX:
         case OsFreeBSD:
-        case OsIOS:
-        case OsTvOS:
-        case OsWatchOS:
         case OsFuchsia:
         case OsKFreeBSD:
         case OsNetBSD:
@@ -994,6 +990,10 @@ ZigLLVM_EnvironmentType target_default_abi(ZigLLVM_ArchType arch, Os os) {
         case OsGLSL450:
         case OsVulkan:
         case OsPlan9:
+        case OsMacOSX:
+        case OsIOS:
+        case OsTvOS:
+        case OsWatchOS:
             return ZigLLVM_UnknownEnvironment;
     }
     zig_unreachable();
diff --git a/src/target.zig b/src/target.zig
index c794ea52b0..14af2675d2 100644
--- a/src/target.zig
+++ b/src/target.zig
@@ -16,8 +16,8 @@ pub const available_libcs = [_]ArchOsAbi{
     .{ .arch = .aarch64, .os = .linux, .abi = .gnu },
     .{ .arch = .aarch64, .os = .linux, .abi = .musl },
     .{ .arch = .aarch64, .os = .windows, .abi = .gnu },
-    .{ .arch = .aarch64, .os = .macos, .abi = .gnu, .os_ver = .{ .major = 11, .minor = 0 } },
-    .{ .arch = .aarch64, .os = .macos, .abi = .gnu, .os_ver = .{ .major = 12, .minor = 0 } },
+    .{ .arch = .aarch64, .os = .macos, .abi = .none, .os_ver = .{ .major = 11, .minor = 0 } },
+    .{ .arch = .aarch64, .os = .macos, .abi = .none, .os_ver = .{ .major = 12, .minor = 0 } },
     .{ .arch = .armeb, .os = .linux, .abi = .gnueabi },
     .{ .arch = .armeb, .os = .linux, .abi = .gnueabihf },
     .{ .arch = .armeb, .os = .linux, .abi = .musleabi },
@@ -70,9 +70,9 @@ pub const available_libcs = [_]ArchOsAbi{
     .{ .arch = .x86_64, .os = .linux, .abi = .gnux32 },
     .{ .arch = .x86_64, .os = .linux, .abi = .musl },
     .{ .arch = .x86_64, .os = .windows, .abi = .gnu },
-    .{ .arch = .x86_64, .os = .macos, .abi = .gnu, .os_ver = .{ .major = 10, .minor = 0 } },
-    .{ .arch = .x86_64, .os = .macos, .abi = .gnu, .os_ver = .{ .major = 11, .minor = 0 } },
-    .{ .arch = .x86_64, .os = .macos, .abi = .gnu, .os_ver = .{ .major = 12, .minor = 0 } },
+    .{ .arch = .x86_64, .os = .macos, .abi = .none, .os_ver = .{ .major = 10, .minor = 0 } },
+    .{ .arch = .x86_64, .os = .macos, .abi = .none, .os_ver = .{ .major = 11, .minor = 0 } },
+    .{ .arch = .x86_64, .os = .macos, .abi = .none, .os_ver = .{ .major = 12, .minor = 0 } },
 };
 
 pub fn libCGenericName(target: std.Target) [:0]const u8 {