first pass at zig build system

 * `zig build --export [obj|lib|exe]` changed to `zig build_obj`,
   `zig build_lib` and `zig build_exe` respectively.
 * `--name` parameter is optional when it can be inferred from the
   root source filename. closes #207
 * `zig build` now looks for `build.zig` which interacts with
   `std.build.Builder` to describe the targets, and then the zig
   build system prints TODO: build these targets. See #204
 * add `@bitcast` which is mainly used for pointer reinterpret
   casting and make explicit casting not do pointer reinterpretation.
   Closes #290
 * fix debug info for byval parameters
 * sort command line help options
 * `std.debug.panic` supports format string printing
 * add `std.mem.IncrementingAllocator`
 * fix const ptr to a variable with data changing at runtime.
   closes #289

3 files changed, 32 insertions, 14 deletions

diff --git a/std/special/build_runner.zig b/std/special/build_runner.zig
new file mode 100644
index 0000000000..73a608487a
--- /dev/null
+++ b/std/special/build_runner.zig
@@ -0,0 +1,18 @@
+const root = @import("@build");
+const std = @import("std");
+const io = std.io;
+const Builder = std.build.Builder;
+const mem = std.mem;
+
+pub fn main(args: [][]u8) -> %void {
+    const zig_exe = args[1];
+    const leftover_args = args[2...];
+
+    // TODO use a more general purpose allocator here
+    var inc_allocator = %%mem.IncrementingAllocator.init(10 * 1024 * 1024);
+    defer inc_allocator.deinit();
+
+    var builder = Builder.init(zig_exe, &inc_allocator.allocator);
+    root.build(&builder);
+    %return builder.make(leftover_args);
+}
diff --git a/std/special/compiler_rt.zig b/std/special/compiler_rt.zig
index 8f61876305..f5c83becc7 100644
--- a/std/special/compiler_rt.zig
+++ b/std/special/compiler_rt.zig
@@ -15,7 +15,7 @@ export fn __udivdi3(a: du_int, b: du_int) -> du_int {
 
 fn du_int_to_udwords(x: du_int) -> udwords {
     @setDebugSafety(this, false);
-    return *(&udwords)(&x);
+    return *@bitcast(&udwords, &x);
 }
 
 export fn __udivmoddi4(a: du_int, b: du_int, maybe_rem: ?&du_int) -> du_int {
@@ -66,7 +66,7 @@ export fn __udivmoddi4(a: du_int, b: du_int, maybe_rem: ?&du_int) -> du_int {
             if (var rem ?= maybe_rem) {
                 r[high] = n[high] % d[high];
                 r[low] = 0;
-                *rem = *(&du_int)(&r[0]);
+                *rem = *@bitcast(&du_int, &r[0]);
             }
             return n[high] / d[high];
         }
@@ -78,7 +78,7 @@ export fn __udivmoddi4(a: du_int, b: du_int, maybe_rem: ?&du_int) -> du_int {
             if (var rem ?= maybe_rem) {
                 r[low] = n[low];
                 r[high] = n[high] & (d[high] - 1);
-                *rem = *(&du_int)(&r[0]);
+                *rem = *@bitcast(&du_int, &r[0]);
             }
             return n[high] >> @ctz(d[high]);
         }
@@ -89,7 +89,7 @@ export fn __udivmoddi4(a: du_int, b: du_int, maybe_rem: ?&du_int) -> du_int {
         // 0 <= sr <= n_uword_bits - 2 or sr large
         if (sr > n_uword_bits - 2) {
             if (var rem ?= maybe_rem) {
-                *rem = *(&du_int)(&n[0]);
+                *rem = *@bitcast(&du_int, &n[0]);
             }
             return 0;
         }
@@ -113,12 +113,12 @@ export fn __udivmoddi4(a: du_int, b: du_int, maybe_rem: ?&du_int) -> du_int {
                     *rem = n[low] & (d[low] - 1);
                 }
                 if (d[low] == 1) {
-                    return *(&du_int)(&n[0]);
+                    return *@bitcast(&du_int, &n[0]);
                 }
                 sr = @ctz(d[low]);
                 q[high] = n[high] >> sr;
                 q[low] = (n[high] << (n_uword_bits - sr)) | (n[low] >> sr);
-                return *(&du_int)(&q[0]);
+                return *@bitcast(&du_int, &q[0]);
             }
             // K X
             // ---
@@ -154,7 +154,7 @@ export fn __udivmoddi4(a: du_int, b: du_int, maybe_rem: ?&du_int) -> du_int {
             // 0 <= sr <= n_uword_bits - 1 or sr large
             if (sr > n_uword_bits - 1) {
                 if (var rem ?= maybe_rem) {
-                    *rem = *(&du_int)(&n[0]);
+                    *rem = *@bitcast(&du_int, &n[0]);
                 }
                 return 0;
             }
@@ -191,17 +191,17 @@ export fn __udivmoddi4(a: du_int, b: du_int, maybe_rem: ?&du_int) -> du_int {
         //      r.all -= d.all;
         //      carry = 1;
         // }
-        const s: di_int = (di_int)(*(&du_int)(&d[0]) - *(&du_int)(&r[0]) - 1) >> (n_udword_bits - 1);
+        const s: di_int = (di_int)(*@bitcast(&du_int, &d[0]) - *@bitcast(&du_int, &r[0]) - 1) >> (n_udword_bits - 1);
         carry = su_int(s & 1);
-        *(&du_int)(&r[0]) -= *(&du_int)(&d[0]) & u64(s);
+        *@bitcast(&du_int, &r[0]) -= *@bitcast(&du_int, &d[0]) & u64(s);
 
         sr -= 1;
     }
-    *(&du_int)(&q[0]) = (*(&du_int)(&q[0]) << 1) | u64(carry);
+    *@bitcast(&du_int, &q[0]) = (*@bitcast(&du_int, &q[0]) << 1) | u64(carry);
     if (var rem ?= maybe_rem) {
-        *rem = *(&du_int)(&r[0]);
+        *rem = *@bitcast(&du_int, &r[0]);
     }
-    return *(&du_int)(&q[0]);
+    return *@bitcast(&du_int, &q[0]);
 }
 
 export fn __umoddi3(a: du_int, b: du_int) -> du_int {
diff --git a/std/special/zigrt.zig b/std/special/zigrt.zig
index 148516eb40..6f7911917d 100644
--- a/std/special/zigrt.zig
+++ b/std/special/zigrt.zig
@@ -1,5 +1,5 @@
 // This file contains functions that zig depends on to coordinate between
-// multiple .o files. The symbols are defined LinkOnce so that multiple
+// multiple .o files. The symbols are defined Weak so that multiple
 // instances of zig_rt.zig do not conflict with each other.
 
 export coldcc fn __zig_panic(message_ptr: &const u8, message_len: usize) -> noreturn {
@@ -11,6 +11,6 @@ export coldcc fn __zig_panic(message_ptr: &const u8, message_len: usize) -> nore
     } else if (@compileVar("os") == Os.freestanding) {
         while (true) {}
     } else {
-        @import("std").debug.panic(message_ptr[0...message_len]);
+        @import("std").debug.panic("{}\n", message_ptr[0...message_len]);
     }
 }