Allow clang to build __clear_cache on ARM.

__clear_cache is special. It needs no signature, but is a real function in
compiler_rt or libgcc.

Patch by Andrew Turner.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@183926 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 0047181..e43a318 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -8687,7 +8687,8 @@
 
   // Builtin functions cannot be defined.
   if (unsigned BuiltinID = FD->getBuiltinID()) {
-    if (!Context.BuiltinInfo.isPredefinedLibFunction(BuiltinID)) {
+    if (!Context.BuiltinInfo.isPredefinedLibFunction(BuiltinID) &&
+        !Context.BuiltinInfo.isPredefinedRuntimeFunction(BuiltinID)) {
       Diag(FD->getLocation(), diag::err_builtin_definition) << FD;
       FD->setInvalidDecl();
     }