since handling this correctly is quite complex, and on some platforms  
requires additional -D options and on some implies linking against a  
different libc, but this works better than just ignoring the option.

The other change passes the -x option across to clang, which allows  
compiling .c files as Objective-C and so on.  For some reason a lot of  
configure scripts seem to be under the misguided impression that this  
is a sensible thing to do."

Patch by David Chisnall!

llvm-svn: 52579