Fix building zig with clang-cl on Windows

[vahur]

When building zig with clang-cl 18 on Windows, there were couple of issues:

1. zig_import macro had too few arguments:

D:\Projects\zig\stage1\zig.h(3377,1): error: too few arguments provided to function-like macro invocation
 3377 | zig_common_float_builtins(32)
      | ^
D:\Projects\zig\stage1\zig.h(3362,5): note: expanded from macro 'zig_common_float_builtins'
 3362 |     zig_expand_concat(zig_expand_import_, zig_expand_has_builtin(zig_libc_name_f##w(fmax)))(zig_f##w, zig_max_f##w, zig_libc_name_f##w(fmax), (zig_f##w x, zig_f##w y), (x, y)) \
      |     ^
D:\Projects\zig\stage1\zig.h(29,37): note: expanded from macro 'zig_expand_concat'
   29 | #define zig_expand_concat(lhs, rhs) zig_concat(lhs, rhs)
      |                                     ^
D:\Projects\zig\stage1\zig.h(28,30): note: expanded from macro 'zig_concat'
   28 | #define zig_concat(lhs, rhs) lhs##rhs
      |                              ^
<scratch space>(15,1): note: expanded from here
   15 | zig_expand_import_1
      | ^
D:\Projects\zig\stage1\zig.h(236,76): note: expanded from macro 'zig_expand_import_1'
  236 | #define zig_expand_import_1(Type, fn_name, libc_name, sig_args, call_args) zig_import_builtin(Type, fn_name, libc_name, sig_args, call_args)
      |                                                                            ^
D:\Projects\zig\stage1\zig.h(228,120): note: expanded from macro 'zig_import_builtin'
  228 | #define zig_import_builtin(Type, fn_name, libc_name, sig_args, call_args) zig_import(Type, fn_name, sig_args, call_args)
      |
       ^
D:\Projects\zig\stage1\zig.h(226,9): note: macro 'zig_import' defined here
  226 | #define zig_import(Type, fn_name, libc_name, sig_args, call_args) zig_extern Type fn_name sig_args;

2. zig_export failed to export symbols with clang-cl.
3. zig2.c compilation failed with an error

In file included from D:\Projects\Misc\zig\build\zig2.c:3:
D:\Projects\zig\stage1\zig.h(3844,11): error: address argument to atomic operation must be a pointer to _Atomic type ('volatile zig_u128 *' (aka 'volatile unsigned __int128 *') invalid)
 3844 |     (void)zig_cmpxchg_strong(obj, expected, expected, zig_memory_order_seq_cst, zig_memory_order_seq_cst, u128, zig_u128);
      |           ^                  ~~~
D:\Projects\zig\stage1\zig.h(3576,85): note: expanded from macro 'zig_cmpxchg_strong'
 3576 | #define zig_cmpxchg_strong(     obj, expected, desired, succ, fail, Type, ReprType) atomic_compare_exchange_strong_explicit(obj, &(expected), desired, succ, fail)
      |                                                                                     ^                                       ~~~
D:\Frameworks\llvm-18\lib\clang\18\include\stdatomic.h(145,49): note: expanded from macro 'atomic_compare_exchange_strong_explicit'
  145 | #define atomic_compare_exchange_strong_explicit __c11_atomic_compare_exchange_strong

With this patch, it is possible to compile zig on Windows with clang as MSVC replacement. Target triple is x86_64-windows-msvc.

Sample build script - build-zig-stage3.cmd:

@echo off
setlocal
call "C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Auxiliary\Build\vcvarsall.bat" x64
SET LLVM_DIR=D:/Frameworks/llvm-18-zig
SET CLANG_DIR=D:/Frameworks/llvm-18
SET CFLAGS=/Oy /GS- /clang:-march=native /clang:-mtune=native /D_CRT_SECURE_NO_WARNINGS -Wno-deprecated-declarations

cd /d D:\Projects\zig
rmdir /s /q build
mkdir build
cd build

cmake ..  ^
  -DCMAKE_BUILD_TYPE=Release ^
  -DCMAKE_C_COMPILER="%CLANG_DIR%/bin/clang-cl.exe" ^
  -DCMAKE_CXX_COMPILER="%CLANG_DIR%/bin/clang-cl.exe" ^
  -DCMAKE_C_FLAGS="%CFLAGS%" ^
  -DCMAKE_CXX_FLAGS="%CFLAGS%" ^
  -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded ^
  -DCMAKE_PREFIX_PATH="%LLVM_DIR%" ^
  -DCMAKE_RC_COMPILER="%CLANG_DIR%/bin/llvm-rc.exe" ^
  -DZIG_USE_LLVM_CONFIG=OFF ^
  -DZIG_STATIC_LLVM=ON ^
  -DZIG_TARGET_TRIPLE=x86_64-windows-msvc ^
  -G Ninja

ninja

[alexrp]

Note that changes to zig.h should be done in lib/zig.h first. They will then eventually flow to stage1/zig.h on the next zig1.wasm update.

cc @kcbanner

[vahur]

@alexrp I updated lib/zig.h with changes from stage1/zig.h. It now compiles with clang-cl even if stage1/zig.h is replaced with the one from lib.

[alexrp]

@alexrp I updated lib/zig.h with changes from stage1/zig.h. It now compiles with clang-cl even if stage1/zig.h is replaced with the one from lib.

You still need to revert the changes to stage1/zig.h. To be clear, that file should never really be touched manually; it is updated when a Zig core team member does zig build update-zig1 to update stage1/zig1.wasm.

(Also, this has merge conflicts that need to be resolved.)

[vahur]

@alexrp I reverted stage1/zig.h and made the suggested changes to lib/zig.h