Index: llvm/trunk/include/llvm/Support/Compiler.h
===================================================================
--- llvm/trunk/include/llvm/Support/Compiler.h
+++ llvm/trunk/include/llvm/Support/Compiler.h
@@ -227,6 +227,8 @@
 /// LLVM_FALLTHROUGH - Mark fallthrough cases in switch statements.
 #if __cplusplus > 201402L && __has_cpp_attribute(fallthrough)
 #define LLVM_FALLTHROUGH [[fallthrough]]
+#elif __has_cpp_attribute(gnu::fallthrough)
+#define LLVM_FALLTHROUGH [[gnu::fallthrough]]
 #elif !__cplusplus
 // Workaround for llvm.org/PR23435, since clang 3.6 and below emit a spurious
 // error when __has_cpp_attribute is given a scoped attribute in C mode.