Clean up a few references to System/. We still have docs/SystemLibrary.html
lying around...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141703 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/ThreadLocal.cpp b/lib/Support/ThreadLocal.cpp
index 6b43048..fdb251c 100644
--- a/lib/Support/ThreadLocal.cpp
+++ b/lib/Support/ThreadLocal.cpp
@@ -79,6 +79,6 @@
 #elif defined( LLVM_ON_WIN32)
 #include "Windows/ThreadLocal.inc"
 #else
-#warning Neither LLVM_ON_UNIX nor LLVM_ON_WIN32 was set in System/ThreadLocal.cpp
+#warning Neither LLVM_ON_UNIX nor LLVM_ON_WIN32 set in Support/ThreadLocal.cpp
 #endif
 #endif