interpret the WASI blob to produce zig2.c and compiler_rt.c

* synchronize zig1.c from zig-wasi external project
 * change the way argv works to avoid absolute paths
 * autodetect isatty
 * compiler_rt: disable some functions when object format is C
 * add missing flag from config.zig.in

The next problem is that compiling compiler_rt.c with gcc gives
"conflicting types" errors for `__eqhf2` and friends.

stage1/config.zig.in

@@ -11,3 +11,4 @@ pub const value_tracing = false;
 pub const have_stage1 = false;
 pub const skip_non_native = false;
 pub const only_c = true;
+pub const force_gpa = false;