[Bug ada/55243] STAMP variable is not defined in t-avr

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55243

--- Comment #16 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-12-10 18:47:13 UTC ---
> > So t-multilib is autogenerated in the source tree during the build???
> 
> Jepp.  Top $(srcdir)/gcc/config/avr/t-multilib reads:
> 
> 
> # Auto-generated Makefile Snip
> # Generated by    : ./gcc/config/avr/genmultilib.awk
> # Generated from  : ./gcc/config/avr/avr-mcus.def
> # Used by         : tmake_file from Makefile and genmultilib

But this is a no-no, the compiler should be buildable with read-only sources
once it is packaged in the release tarballs.

> Rationale is that avr-gcc supports an, IMHO, insane number of -mmcu=<device>. 
> In order to keep various parts of the compiler in sync, some bits are
> auto-generated, amongst them documentation, t-multilib and .opt parts.
> 
> Procedure is a move-if-change scheme, i.e. the auto-generated files are in the
> repository and the procedure to build them is similar to building configure
> from configure.ac and then putting both configure.ac /and/ configure into the
> repo.

Building configure from configure.c isn't done at build time.

Either you generate t-multilib like configure and you can put it in $(srcdir)
or you generate it at build time and you must put it in $(builddir).