[llvm] [gn] Add "/Zc:preprocessor" build flag on windows (PR #108252)

[via llvm-commits]

https://github.com/GkvJwa updated https://github.com/llvm/llvm-project/pull/108252

>From 8f9a82e8ad1ab67c01dd7518b8ed92ad2e2beeb9 Mon Sep 17 00:00:00 2001
From: GkvJwa <gkvjwa at gmail.com>
Date: Thu, 12 Sep 2024 01:05:15 +0800
Subject: [PATCH 1/2] [gn] Add /Zc:preprocessor on windows

---
 llvm/utils/gn/build/BUILD.gn | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/llvm/utils/gn/build/BUILD.gn b/llvm/utils/gn/build/BUILD.gn
index 1ccaefdc21c822..11d28f6be6bce9 100644
--- a/llvm/utils/gn/build/BUILD.gn
+++ b/llvm/utils/gn/build/BUILD.gn
@@ -183,6 +183,9 @@ config("compiler_defaults") {
     cflags += [ "/EHs-c-" ]
     cflags_cc += [ "/std:c++17" ]
 
+    # expand __VA_ARGS__ in "OPTION(...) LLVM_MAKE_OPT_ID(__VA_ARGS__)"
+    cflags += [ "/Zc:preprocessor" ]
+
     # cl.exe doesn't set __cplusplus correctly by default.
     # clang-cl gets it right by default, so don't needlessly add the flag there.
     if (!is_clang) {

>From 6b53d8db139a456cc9a4db172784a65ac2b54101 Mon Sep 17 00:00:00 2001
From: GkvJwa <gkvjwa at gmail.com>
Date: Thu, 12 Sep 2024 16:30:20 +0800
Subject: [PATCH 2/2] Only use cl.exe add this flags

---
 llvm/utils/gn/build/BUILD.gn | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/llvm/utils/gn/build/BUILD.gn b/llvm/utils/gn/build/BUILD.gn
index 11d28f6be6bce9..2724ccfa0ce57e 100644
--- a/llvm/utils/gn/build/BUILD.gn
+++ b/llvm/utils/gn/build/BUILD.gn
@@ -183,12 +183,11 @@ config("compiler_defaults") {
     cflags += [ "/EHs-c-" ]
     cflags_cc += [ "/std:c++17" ]
 
-    # expand __VA_ARGS__ in "OPTION(...) LLVM_MAKE_OPT_ID(__VA_ARGS__)"
-    cflags += [ "/Zc:preprocessor" ]
-
     # cl.exe doesn't set __cplusplus correctly by default.
     # clang-cl gets it right by default, so don't needlessly add the flag there.
     if (!is_clang) {
+      # expand __VA_ARGS__ in "OPTION(...) LLVM_MAKE_OPT_ID(__VA_ARGS__)"
+      cflags += [ "/Zc:preprocessor" ]
       cflags_cc += [ "/Zc:__cplusplus" ]
     }