configure: Avoid unnecessary constraints on executables for $build.

The executables for GCC's c-family compilers must be built with no-PIE
because they use PCH and the current model for this requires that the
exe is always lauched at the same address.  Since the other language
compilers share code with the c-family this constraint is also applied
to them.

However, the executables that run on $build (generators, and parsers
for md and def files) need not have any such constraint they do not
consume PCH files.

This change simplifies the configuration and Makefile content by
removing the code enforcing no-PIE on these exes.  This also fixes a
bootstrap issue with some Darwin versions and clang as the bootstrap
compiler,  where -no-PIE causes the correct relocation model to be
switched off leading to invalid user-space code.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>

gcc/ChangeLog:

	* Makefile.in: Remove variables related to applying no-PIE
	to the exes on $build.
	* configure: Regenerate.
	* configure.ac: Remove configuration related to applying
	no-PIE to the exes on $build.