versioner: cache -cc1 flags generated by the clang Driver.

Profiling showed that majority of time spent by versioner was being
spent in the x86 and x86_64 driver statting random files in /usr/lib,
looking for a toolchain. Hardcode a list of per-target flags which
correspond to a subset of the ones generated by clang, and use those
instead of calling out to Driver.

This changes the result of `time versioner` from:
    versioner  156.57s user 1180.08s system 4109% cpu 32.525 total
to:
    versioner  109.12s user 17.43s system 2433% cpu 5.201 total

Bug: http://b/32748936
Test: python run_tests.py
Change-Id: I7d254a105bf1a283cbba0546321b04e308e703d1
diff --git a/tools/versioner/src/versioner.h b/tools/versioner/src/versioner.h
index 9547f2c..97b1509 100644
--- a/tools/versioner/src/versioner.h
+++ b/tools/versioner/src/versioner.h
@@ -23,6 +23,7 @@
 #include <unordered_set>
 
 extern bool verbose;
+extern bool add_include;
 
 #define D(...)             \
   do {                     \