bug#7873: Automake should support adding to DejaGnu site.exp

[Rainer Orth]

Currently, Automake doesn't support adding package-specific content to
the site.exp file generated for DejaGnu testsuites.  In GCC alone, three
testsuites need that facility and have to override the
Automake-generated target wholesale to achieve what they need:

boehm-gc/testsuite/Makefile.am
libjava/testsuite/Makefile.am
libstdc++-v3/testsuite/Makefile.am

These Makefile.am's carry the following comment:

# We need more things in site.exp, but automake completely controls the
# creation of that file; there's no way to append to it without messing up
# the dependancy chains.  So we overrule automake.  This rule is exactly
# what it would have generated, plus our own additions.

Since in the future it is easily possible that the target/commands
generated by Automake deviate from what is currently emitted there,
there should be a Automake facility to directly support adding to the
generated site.exp.

Thanks.
        Rainer

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Rainer Orth, Center for Biotechnology, Bielefeld University