LoongArch: When checking whether the assembler supports conditional branch...

LoongArch: When checking whether the assembler supports conditional branch relaxation, add compilation parameter "--fatal-warnings" to the assembler.

In binutils 2.40 and earlier versions, only a warning will be reported
when a relocation immediate value is out of bounds. As a result,
the value of the macro HAVE_AS_COND_BRANCH_RELAXATION will also be
defined as 1 when the assembler does not support conditional branch
relaxation. Therefore, add the compilation option "--fatal-warnings"
to avoid this problem.

gcc/ChangeLog:

	* configure: Regenerate.
	* configure.ac: Add parameter "--fatal-warnings" to assemble
	when checking whether the assemble support conditional branch
	relaxation.