avoid changing NaNs in sqrt (x86 asm) to satisfy c99 f.9 recommendation

src/math/i386/sqrt.s

@@ -10,6 +10,10 @@ sqrt:	fldl 4(%esp)
 	and $0x7ff,%ecx
 	cmp $0x400,%ecx
 	jnz 1f
+	mov 8(%esp),%ecx
+	or $0xffff8000,%ecx
+	inc %ecx
+	jz 1f
 	and $0x200,%eax
 	sub $0x100,%eax
 	sub %eax,(%esp)