Fix erroneous -Wmissing-prototypes for Win32 entry points (#98105)

Fixes #94366.

Author: MaxEW707

clang/docs/ReleaseNotes.rst

@@ -686,6 +686,9 @@ Improvements to Clang's diagnostics
 
 - Clang now shows implicit deduction guides when diagnosing overload resolution failure. #GH92393.
 
+- Clang no longer emits a "no previous prototype" warning for Win32 entry points under ``-Wmissing-prototypes``.
+  Fixes #GH94366.
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/lib/Sema/SemaDecl.cpp

@@ -15222,6 +15222,9 @@ ShouldWarnAboutMissingPrototype(const FunctionDecl *FD,
       if (II->isStr("main") || II->isStr("efi_main"))
         return false;
 
+  if (FD->isMSVCRTEntryPoint())
+    return false;
+
   // Don't warn about inline functions.
   if (FD->isInlined())
     return false;

clang/test/Sema/no-warn-missing-prototype.c

@@ -1,5 +1,6 @@
 // RUN: %clang_cc1 -fsyntax-only -Wmissing-prototypes -x c -ffreestanding -verify %s
 // RUN: %clang_cc1 -fsyntax-only -Wmissing-prototypes -x c++ -ffreestanding -verify %s
+// RUN: %clang_cc1 -fms-compatibility -fsyntax-only -Wmissing-prototypes -x c++ -ffreestanding -triple=x86_64-pc-win32 -verify -DMS %s
 // expected-no-diagnostics
 int main() {
   return 0;
@@ -8,3 +9,21 @@ int main() {
 int efi_main() {
   return 0;
 }
+
+#ifdef MS
+int wmain(int, wchar_t *[], wchar_t *[]) {
+  return 0;
+}
+
+int wWinMain(void*, void*, wchar_t*, int) {
+  return 0;
+}
+
+int WinMain(void*, void*, char*, int) {
+  return 0;
+}
+
+bool DllMain(void*, unsigned, void*) {
+  return true;
+}
+#endif