MFC r323001:

In compiler-rt, a few assembler implementations for i386 floating point
conversion functions use SSE2 instructions, but these are not guarded by
#ifdef SSE2, and there is no implementation using general purpose
registers. For these functions, use the generic C variants instead,
otherwise they will cause SIGILL on older processors.

Reported by: bsdpr@phoe.frmug.org
PR: 221733

MFC r323014:

Follow-up to r323001: if the actually selected CPUTYPE is capable of
SSE2 instructions, we can use them.

Suggested by: jkim