llvmpipe: add cc clobber to inline asm

The bsr instruction modifies flags, so that needs to be indicated to the
compiler. No effect on generated code, but still needed for correctness.

Reviewed-by: Roland Scheidegger <sroland@vmware.com>

src/gallium/drivers/llvmpipe/lp_setup_tri.c

@@ -734,7 +734,8 @@ floor_pot(uint32_t n)
 
    __asm__("bsr %1,%0"
           : "=r" (n)
-          : "rm" (n));
+          : "rm" (n)
+          : "cc");
    return 1 << n;
 #else
    n |= (n >>  1);