i386: Fix ICE with -fsplit-stack -mcmodel=large [PR112686]

For -mcmodel=large, we have to load function address to a register.

	PR target/112686

gcc/ChangeLog:

	* config/i386/i386.cc (ix86_expand_split_stack_prologue): Load
	function address to a register for ix86_cmodel == CM_LARGE.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr112686.c: New test.