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
@@ -736,7 +736,7 @@
   endif()
 
   append("-Wextra -Wno-unused-parameter -Wwrite-strings" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
-  append("-Wcast-qual" CMAKE_CXX_FLAGS)
+  append("-Wcast-qual" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 
   # Turn off missing field initializer warnings for gcc to avoid noise from
   # false positives with empty {}. Turn them on otherwise (they're off by
diff --git a/llvm/lib/Support/regcomp.c b/llvm/lib/Support/regcomp.c
--- a/llvm/lib/Support/regcomp.c
+++ b/llvm/lib/Support/regcomp.c
@@ -329,7 +329,15 @@
 
 	/* set things up */
 	p->g = g;
+	/* suppress warning from the following explicit cast. */
+#ifdef __GNUC__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wcast-qual"
+#endif /* __GNUC__ */
 	p->next = (char *)pattern;	/* convenience; we do not modify it */
+#ifdef __GNUC__
+#pragma GCC diagnostic pop
+#endif /* __GNUC__ */
 	p->end = p->next + len;
 	p->error = 0;
 	p->ncsalloc = 0;