diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -668,6 +668,11 @@
   if (LLVM_ENABLE_PEDANTIC AND LLVM_COMPILER_IS_GCC_COMPATIBLE)
     append("-pedantic" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
     append("-Wno-long-long" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+
+    # GCC warns about redundant toplevel semicolons (enabled by -pedantic
+    # above), while Clang doesn't. Enable the corresponding Clang option to
+    # pick up on these even in builds with Clang.
+    add_flag_if_supported("-Wc++98-compat-extra-semi" C98_COMPAT_EXTRA_SEMI_FLAG)
   endif()
 
   add_flag_if_supported("-Wimplicit-fallthrough" IMPLICIT_FALLTHROUGH_FLAG)