[testsuite] [x86] double copysign requires -msse2

[testsuite] [x86] double copysign requires -msse2

SSE_FLOAT_MODE_P only holds for DFmode with SSE2, and that's a
condition for copysign<mode>3 to be available under TARGET_SSE_MATH.

Various copysign testcases use -msse -mfpmath=sse on ia32 to enable
the copysign builtins and patterns, but that would only be enough if
the tests were limited to floats.  Since they test doubles as well, we
need -msse2 instead of -msse.

for  gcc/testsuite/ChangeLog

	* gcc.dg/fold-copysign-1.c: Bump to sse2 on ia32.
	* gcc.dg/pr55152-2.c: Likewise.
	* gcc.dg/tree-ssa/abs-4.c: Likewise.
	* gcc.dg/tree-ssa/backprop-6.c: Likewise.