[clang] prevent -Wunknown-warning-option with older clangs

Author: nico

clang/include/clang/Basic/LangOptions.def

@@ -348,13 +348,13 @@ COMPATIBLE_LANGOPT(ExpStrictFP, 1, false, "Enable experimental strict floating p
 BENIGN_LANGOPT(RoundingMath, 1, false, "Do not assume default floating-point rounding behavior")
 BENIGN_ENUM_LANGOPT(FPExceptionMode, FPExceptionModeKind, 2, FPE_Default, "FP Exception Behavior Mode type")
 
-#if defined(__clang__)
+#if defined(__clang__) && defined( __has_warning ) && __has_warning("-Wpreferred-type-bitfield-enum-conversion")
 // FIXME: Remove this once the warning is fixed, https://llvm.org/PR137600
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wpreferred-type-bitfield-enum-conversion"
 #endif
 BENIGN_ENUM_LANGOPT(FPEvalMethod, FPEvalMethodKind, 3, FEM_UnsetOnCommandLine, "FP type used for floating point arithmetic")
-#if defined(__clang__)
+#if defined(__clang__) && defined( __has_warning ) && __has_warning("-Wpreferred-type-bitfield-enum-conversion")
 #pragma clang diagnostic pop
 #endif
 

clang/include/clang/Basic/LangOptions.h

@@ -78,14 +78,14 @@ class LangOptionsBase {
 
   LangOptionsBase() = default;
 
-#if defined(__clang__)
+#if defined(__clang__) && defined( __has_warning ) && __has_warning("-Wpreferred-type-bitfield-enum-conversion")
 // FIXME: Remove this once the warning is fixed, https://llvm.org/PR137600
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wpreferred-type-bitfield-enum-conversion"
 #endif
   LangOptionsBase(const LangOptionsBase&) = default;
   LangOptionsBase& operator=(const LangOptionsBase&) = default;
-#if defined(__clang__)
+#if defined(__clang__) && defined( __has_warning ) && __has_warning("-Wpreferred-type-bitfield-enum-conversion")
 #pragma clang diagnostic pop
 #endif