PCH test errors

[Andrew Stubbs]

I'm testing amdgcn-amdhsa, and I get lot of PCH test failures with 
errors like this:

gcc.dg/pch/common-1.c:1:22: error: one or more PCH files were found, but 
they were invalid
gcc.dg/pch/common-1.c:1:22: error: use -Winvalid-pch for more information
gcc.dg/pch/common-1.c:1:10: fatal error: common-1.h: No such file or 
directory

It may affect other targets, but I've not tested those. Has anybody else 
seen this issue?

I've done a bisect, and found it first starts with this:

    1dedc12d1: revamp dump and aux output names

I've also seen others complaining about other issues with this commit, 
so this may be a duplicate issue, somehow.

Andrew