V3 PATCH speed up cached math configure checks

[Robert Lipe]

> This (seemingly-redundant) check gains a large speedup when the math
> declaration/linkage checks have been cached from a previous run.  (See the
> "slow configure" thread on the v3 list.)

This does make a notable different. libstdc++v3 (re)configuration is
still unpleasantly slow but now less so.

Thank you for your efforts in conserving bananas. :-)

RJL

> 2000-12-06  Phil Edwards  <pme@sources.redhat.com>
> 
> 	* acinclude.m4 (GLIBCPP_CHECK_*_DECL_AND_LINKAGE_*):  Pre-test
> 	  whether the cached result is present.
> 	* aclocal.m4:  Regenerate.
> 	* configure:  Regenerate.
> 	* Makefile.in:  Regenerate.
> 	* libio/Makefile.in:  Regenerate.
> 	* libmath/Makefile.in:  Regenerate.
> 	* libsupc++/Makefile.in:  Regenerate.
> 	* src/Makefile.in:  Regenerate.