Fix a typo (builting -> builtin).

Patch by Afriza N. Arief!

llvm-svn: 149822
diff --git a/clang/docs/tools/clang.pod b/clang/docs/tools/clang.pod
index 964b143..8f61568 100644
--- a/clang/docs/tools/clang.pod
+++ b/clang/docs/tools/clang.pod
@@ -465,7 +465,7 @@
 =item B<-nostdlibinc>
 
 Do not search the standard system directories for include files, but do search
-compiler builting include directories.
+compiler builtin include directories.
 
 =item B<-nobuiltininc>