Making libstdc++-v3 configure faster

["Kaveh R. Ghazi" <ghazi at caip dot rutgers dot edu>]

I think this might have been discussed, but configuring libstdc++-v3
is very slow for me on Irix6.  It spends more time configuring than it
does bootstrapping and running the testsuite combined.  It seems to
spend a lot of time checking for the various math decl and linkage
functions.  IIRC, someone mentioned that one reason it is slow is that
is does a whole lot of AC_LANG_SAVE/AC_LANG_RESTORE calls.  Indeed,
the macro is written analogous to this:

loop over functions
{
  AC_LANG_SAVE
  AC_LANG_CPLUSPLUS
  do_test_for_decl
  AC_LANG_RESTORE
  if (decl) do_test_for_linkage
}

If indeed AC_LANG_SAVE/AC_LANG_RESTORE is expensive, it seems to me
that it would make a whole lot more sense to write it like this:

AC_LANG_SAVE
AC_LANG_CPLUSPLUS
loop over functions
{
  do_test_for_decl
}
AC_LANG_RESTORE
loop over functions
{
  if (decl) do_test_for_linkage
}

Thoughts/comments?

--
Kaveh R. Ghazi			Engagement Manager / Project Services
ghazi@caip.rutgers.edu		Qwest Internet Solutions