Append -w when LLVM_ENABLE_WARNINGS is Off.

[v.g.vassilev]

Summary

This is very useful for projects which embed LLVM in their codebases.

[yaron.keren]

cmake/modules/HandleLLVMOptions.cmake

562

note this is an else to
if (LLVM_ENABLE_WARNINGS AND (LLVM_COMPILER_IS_GCC_COMPATIBLE OR CLANG_CL))
so for non-gcc non-clang_cl compilers you'd also end up here.

shouldn't the condition be
if (LLVM_COMPILER_IS_GCC_COMPATIBLE AND NOT LLVM_ENABLE_WARNINGS)

[v.g.vassilev]

Ah good point. Thanks!

[rnk]

lgtm

[v.g.vassilev]

Landed in r300100.

cmake/modules/HandleLLVMOptions.cmake

CHECK_C_SOURCE_COMPILES("// \\\\\\n//\\nint main() {return 0;}"
                           C_WCOMMENT_ALLOWS_LINE_WRAP)
   set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
   if (NOT C_WCOMMENT_ALLOWS_LINE_WRAP)
     append("-Wno-comment" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
   endif()
 
   # Enable -Wstring-conversion to catch misuse of string literals.
   add_flag_if_supported("-Wstring-conversion" STRING_CONVERSION_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)
+  append("-w" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+endif()
+
 macro(append_common_sanitizer_flags)
   if (NOT MSVC)
     # Append -fno-omit-frame-pointer and turn on debug info to get better
     # stack traces.
     add_flag_if_supported("-fno-omit-frame-pointer" FNO_OMIT_FRAME_POINTER)
     if (NOT uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG" AND
         NOT uppercase_CMAKE_BUILD_TYPE STREQUAL "RELWITHDEBINFO")
       add_flag_if_supported("-gline-tables-only" GLINE_TABLES_ONLY)