compiler rebuild invalidates precompiled header

["Jan Beulich" <JBeulich at novell dot com>]

Trying to run the libstdc++ testsuite after a couple of rebuilds to the
compiler all I got was internal compiler errors for each and every
compiled file. Investigating this, I had to learn that the precompiled
header stores not just configuration values, but also pointers created
during the previous build (e.g. into the compiler image itself). This
would be fine, if the precompiled header would be considered invalid by
a compiler build different from the one that created it. That, however,
is not done, and what I'm trying to find out is whether this is
intentional (in which case I'd consider precompiled headers useless for
anyone trying to work on the compiler itself), and if so if there is any
suggested workaround for this (other than manually deleting the
precompiled headers each time the compiler gets rebuilt).
Obviously, I'd consider this a bug with the suggested solution of
adding a timestamp (or even better a random value of good quality) to
the compiler that it then stores into the precompiled header and
verifies when it loads it).

Thanks, Jan