[Bug pch/62001] Many tests fail with PCH

[dominiq at lps dot ens.fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62001

--- Comment #2 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
As reported in PR61250, I see also random PCH failures on darwin, but much
fewer:

g++.dg/pch/pch.C and gcc.dg/pch/save-temps-1.c only.