llvmpipe: Work without sse2 if llvm is new enough

At least on llvm 3.2 this appears to work fine.  Tested on an Athlon XP
2600+, which has sse and 3dnow but not sse2.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
Signed-off-by: Adam Jackson <ajax@redhat.com>

src/gallium/drivers/llvmpipe/lp_screen.c

@@ -485,9 +485,10 @@ llvmpipe_create_screen(struct sw_winsys *winsys)
 {
    struct llvmpipe_screen *screen;
 
-#ifdef PIPE_ARCH_X86
-   /* require SSE2 due to LLVM PR6960. */
    util_cpu_detect();
+
+#if defined(PIPE_ARCH_X86) && HAVE_LLVM < 0x0302
+   /* require SSE2 due to LLVM PR6960. */
    if (!util_cpu_caps.has_sse2)
        return NULL;
 #endif