Ignore unknown -fno-builtin-*.

This matches gcc's behavior.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@191434 91177308-0d34-0410-b5e6-96231b3b80d8
Remove -fbuiltin-strcat and -fbuiltin-strcpy.

These options don't exist in gcc and clang was not handling them.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@191435 91177308-0d34-0410-b5e6-96231b3b80d8
Mark an impossible path as unreachable to pacify GCC.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@191436 91177308-0d34-0410-b5e6-96231b3b80d8
Remove fno_builtin_strcat and fno_builtin_strcpy.

They are already handled by the generic fno_bultin_, which also
avoids unused warnings.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@191437 91177308-0d34-0410-b5e6-96231b3b80d8