Driver: ignore -fno-objc-arc-exception when -fno-objc-arc set

Sometime clang would be supplied -fobjc-arc -f(no)objc-arc-exceptions
and then later disable ARC with -fno-objc-arc, which only negate first
option, but not the latter, resulting usused argument warning.  Silence
this warning only when -fno-objc-arc option is present.

Patch by Onha Choe!

llvm-svn: 293014