update std code for MacOS

closes #264

std/bootstrap.zig

@@ -2,8 +2,6 @@
 
 const root = @import("@root");
 const std = @import("std");
-const linux = std.linux;
-const cstr = std.cstr;
 
 const want_start_symbol = switch(@compileVar("os")) {
     Os.linux => true,
@@ -11,6 +9,11 @@ const want_start_symbol = switch(@compileVar("os")) {
 };
 const want_main_symbol = !want_start_symbol;
 
+const exit = switch(@compileVar("os")) {
+    Os.linux => std.linux.exit,
+    Os.darwin => std.darwin.exit,
+};
+
 var argc: usize = undefined;
 var argv: &&u8 = undefined;
 
@@ -35,14 +38,14 @@ fn callMain() -> %void {
     const args = @alloca([]u8, argc);
     for (args) |_, i| {
         const ptr = argv[i];
-        args[i] = ptr[0...cstr.len(ptr)];
+        args[i] = ptr[0...std.cstr.len(ptr)];
     }
     return root.main(args);
 }
 
 fn callMainAndExit() -> unreachable {
-    callMain() %% linux.exit(1);
-    linux.exit(0);
+    callMain() %% exit(1);
+    exit(0);
 }
 
 export fn main(c_argc: i32, c_argv: &&u8) -> i32 {

std/darwin.zig

@@ -48,6 +48,11 @@ pub const SIGPWR    = 30;
 pub const SIGSYS    = 31;
 pub const SIGUNUSED = SIGSYS;
 
+pub fn exit(status: usize) -> unreachable {
+    arch.syscall1(arch.SYS_exit, status);
+    @unreachable()
+}
+
 /// Get the errno from a syscall return value, or 0 for no error.
 pub fn getErrno(r: usize) -> usize {
     const signed_r = *(&isize)(&r);
@@ -67,7 +72,7 @@ pub fn open_c(path: &const u8, flags: usize, perm: usize) -> usize {
 }
 
 pub fn open(path: []const u8, flags: usize, perm: usize) -> usize {
-    var buf: [path.len + 1]u8 = undefined;
+    const buf = @alloca(u8, path.len + 1);
     @memcpy(&buf[0], &path[0], path.len);
     buf[path.len] = 0;
     return open_c(buf.ptr, flags, perm);

std/darwin_x86_64.zig

@@ -11,6 +11,7 @@ pub const SYSCALL_CLASS_DIAG = 4; // Diagnostics
 
 // TODO: use the above constants to create the below values
 
+pub const SYS_exit = 0x2000001;
 pub const SYS_read = 0x2000003;
 pub const SYS_write = 0x2000004;
 pub const SYS_open = 0x2000005;