Change the library search path when using --with-advance-toolchain

Change the library search path when using --with-advance-toolchain

From: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>

Remove all -L directories from LINK_OS_EXTRA_SPEC32 and
LINK_OS_EXTRA_SPEC64 so that user directories specified at
build time have higher preference over the advance toolchain libraries.

Set MD_STARTFILE_PREFIX to $prefix/lib/ and MD_STARTFILE_PREFIX_1 to
$at/lib/ so that a compiler library has preference over the Advance
Toolchain libraries.

	* config.gcc: Move -L usage from LINK_OS_EXTRA_SPEC32 and
	LINK_OS_EXTRA_SPEC64 to MD_STARTFILE_PREFIX and
	MD_STARTFILE_PREFIX_1 when using --with-advance-toolchain.

From-SVN: r276702