roafteriniter: Add files from ${LINUX}/scripts/gcc-plugins

gcc-common.h and gcc-generate-gimple-pass.h contain some convinience
functions that are useful when writing GCC plugins. These files allow
for writing the plugins in C, even though the GCC API changed to use
C++ after GCC 4.9.

BUG=chromium:860068
TEST=None

Change-Id: I360204a6cdfff073dd5cbd36c2809acd19389a83
Reviewed-on: https://chromium-review.googlesource.com/1244401
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Commit-Ready: Zubin Mithra <zsm@chromium.org>
Tested-by: Zubin Mithra <zsm@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
2 files changed