Use aclocal to generate GDB's aclocal.m4 script.

Use aclocal to generate GDB's aclocal.m4 script.
* acinclude.m4: New file, containing the hand-written local macro
definitions that used to be in aclocal.m4.  Don't sinclude
../bfd/aclocal.m4 any more; running aclocal in this directory will
get us the definitions we need.  HOWEVER: Do sinclude
../bfd/acinclude.m4, because we need the definition of
BFD_NEED_DECLARATION.
* aclocal.m4: Regenerated by aclocal.
* configure: Regenerated by autoconf.