gcc: check if target install name equals the full driver name

gcc: check if target install name equals the full driver name

When a major version program suffix is specified, along with
--with-gcc-major-version-only, GCC tries to install $TRIPLE-gcc-tmp into
the destination BINDIR and link it to TRIPLE-gcc-SUFFIX. However this
executable is installed in the previous step, thus leaving the gcc-tmp
unmodified.

This is because when --program-suffix=15 (any major version) and
--with-gcc-major-version-only, $(version) will be the major version
number, thus making FULL_DRIVER_NAME and GCC_TARGET_INSTALL_NAME
identical to each other. We check if these two is identical and skip the
latter step if they are.

gcc/
	PR bootstrap/105664
	* Makefile.in (install-driver): detect name collision when
	installing the driver program.

Signed-off-by: Xinhui Yang <cyan@cyano.uk>