Build LLVM with -Wstrict-prototypes enabled

Clang 5 supports -Wstrict-prototypes. We should use it to catch any C
declarations that declare a non-prototype function.

rdar://33705313

Differential Revision: https://reviews.llvm.org/D36669


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@312240 91177308-0d34-0410-b5e6-96231b3b80d8

cmake/modules/HandleLLVMOptions.cmake

@@ -581,6 +581,8 @@ if (LLVM_ENABLE_WARNINGS AND (LLVM_COMPILER_IS_GCC_COMPATIBLE OR CLANG_CL))
 
   # Enable -Wstring-conversion to catch misuse of string literals.
   add_flag_if_supported("-Wstring-conversion" STRING_CONVERSION_FLAG)
+  # Enable -Wstrict-prototypes to catch incorrectly declared functions in C.
+  add_flag_if_supported("-Wstrict-prototypes" STRICT_PROTOTYPES_FLAG)
 endif (LLVM_ENABLE_WARNINGS AND (LLVM_COMPILER_IS_GCC_COMPATIBLE OR CLANG_CL))
 
 if (LLVM_COMPILER_IS_GCC_COMPATIBLE AND NOT LLVM_ENABLE_WARNINGS)