i386 PIE: accept @GOTOFF in load/store multi base address

Looking at the code generated for sse2-{load,store}-multi.c with PIE,
I realized we could use UNSPEC_GOTOFF as a base address, and that this
would enable the test to use the vector insns expected by the tests
even with PIC, so I extended the base + offset logic used by the SSE2
multi-load/store peepholes to accept reg + symbolic base + offset too,
so that the test generated the expected insns even with PIE.


for  gcc/ChangeLog

	* config/i386/i386.cc (symbolic_base_address_p,
	base_address_p): New, factored out from...
	(extract_base_offset_in_addr): ... here and extended to
	recognize REG+GOTOFF, as in gcc.target/i386/sse2-load-multi.c
	and sse2-store-multi.c with PIE enabled by default.