clang: Exclude efi_main from -Wmissing-prototypes

When compiling UEFI applications, the main function is named
efi_main() instead of main(). Let's exclude efi_main() from
-Wmissing-prototypes as well to avoid warnings when working
on UEFI applications.

Differential Revision: https://reviews.llvm.org/D95746

Author: DaanDeMeyer

clang/lib/Sema/SemaDecl.cpp

@@ -13873,7 +13873,7 @@ ShouldWarnAboutMissingPrototype(const FunctionDecl *FD,
   // Don't warn about 'main'.
   if (isa<TranslationUnitDecl>(FD->getDeclContext()->getRedeclContext()))
     if (IdentifierInfo *II = FD->getIdentifier())
-      if (II->isStr("main"))
+      if (II->isStr("main") || II->isStr("efi_main"))
         return false;
 
   // Don't warn about inline functions.

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

@@ -4,3 +4,7 @@
 int main() {
   return 0;
 }
+
+int efi_main() {
+  return 0;
+}