i386: Remove unneeded assignments when triggering SSE exceptions

According to "Intel 64 and IA32 Arch SDM, Vol. 3:

"Because SIMD floating-point exceptions are precise and occur immediately,
the situation does not arise where an x87 FPU instruction, a WAIT/FWAIT
instruction, or another SSE/SSE2/SSE3 instruction will catch a pending
unmasked SIMD floating-point exception."

Remove unneeded assignments to volatile memory.

libgcc/ChangeLog:

	* config/i386/sfp-exceptions.c (__sfp_handle_exceptions) [__SSE_MATH__]:
	Remove unneeded assignments to volatile memory.

libatomic/ChangeLog:

	* config/x86/fenv.c (__atomic_feraiseexcept) [__SSE_MATH__]:
	Remove unneeded assignments to volatile memory.

libgfortran/ChangeLog:

	* config/fpu-387.h (local_feraiseexcept) [__SSE_MATH__]:
	Remove unneeded assignments to volatile memory.