configure.ac (--with-build-config): New.

configure.ac (--with-build-config): New.

ChangeLog:
* configure.ac (--with-build-config): New.  Set BUILD_CONFIG.
Default to bootstrap-debug only if compare-debug works.
* configure: Rebuilt.
* Makefile.tpl: Make BUILD_CONFIG configure-configurable.
* Makefile.in: Rebuilt.
contrib/ChangeLog:
* bootstrap-debug-big.mk (STAGE2_CFLAGS): Drop -gtoggle.
* bootstrap-debug-lean.mk: Update comments.
(STAGE2_CFLAGS): Likewise.
(do-compare): Don't override.
gcc/ChangeLog:
* doc/invoke.texi (BUILD_CONFIG): Document --with-build-config.
(bootstrap-debug): Explain conditions in which it becomes default.
(bootstrap-debug-big): Rather than duplicate bootstrap-debug,
make it add to it.

From-SVN: r151367