Edward Z. Yang authored Dec 27, 2014 and Herbert Valerio Riedel committed Jan 09, 2015

Where we track timestamps of object files, also track timestamps
for interface files.  When -fno-code -fwrite-interface is enabled, use
the interface file timestamp as an extra check to see if the files are
up-to-date.  We had to apply this logic to one-shot and make modes.

This fix would be good to merge into 7.10; it makes using -fno-code
-fwrite-interface for flywheel type checking usable.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Addresses #9243

(cherry picked from commit 2223e196)