Downgrade bogus ExtWarn on duplicate 'friend' specifier to a Warning, and add a
Warning for a duplicate 'constexpr' specifier.


git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@198956 91177308-0d34-0410-b5e6-96231b3b80d8
Use the simpler version of llvm::sys::fs::remove when possible.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@198957 91177308-0d34-0410-b5e6-96231b3b80d8