[foreign] RFR clang built-in header files from config path

[Sundararajan Athijegannathan]

Hi,

Avoiding checked-in stdarg.h and stddef.h as suggested in earlier 
review. Copying stddef.h and stdarg.h from configured clang path.

http://cr.openjdk.java.net/~sundar/builtin_headers_from_clang_config/webrev.00/

Thanks,
-Sundar