To make them meaningful, it's useful to check "clang". Use
-no-canonical-prefixes to support distributions that symlink %clang to an
executable with a filename not ending in "clang".
Added supporting CC_PRINT_PROC_STAT and CC_PRINT_PROC_STAT_FILE
environment variables to trigger clang driver reporting the process
statistics into specified file (alternate for -fproc-stat-report
option).
Differential Revision: https://reviews.llvm.org/D97094