llvm-config: Fix typo in help message introduced with r197664.

Thanks, Vinson Lee!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197996 91177308-0d34-0410-b5e6-96231b3b80d8
gold-plugin.cpp: Use form of <plugin-api.h>, since it is external header.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197997 91177308-0d34-0410-b5e6-96231b3b80d8