Ignore unused --serialize-diagnostics option when using llvm-gcc.

llvm-gcc doesn't handle --serialize-diagnostics so when compiling i386
kernel/kext code with -Werror, you get an error about that option being
unused.  Claim the argument to prevent this from breaking builds.
<rdar://problem/11161933>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@153854 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed