unittests/ASM: Test pfacc simple addition

unittests/ASM/FEX_bugs/PFACC_MMXWidth.asm

@@ -0,0 +1,25 @@
+%ifdef CONFIG
+{
+  "RegData": {
+    "MM0": "0x40e0000040400000"
+  },
+  "HostFeatures": ["3DNOW"]
+}
+%endif
+
+femms
+movq mm0, [rel .dst_value]
+movq mm1, [rel .src_value]
+
+pfacc mm0, mm1
+
+hlt
+
+align 8
+.dst_value:
+dd 0x3f800000 ; 1.0
+dd 0x40000000 ; 2.0
+
+.src_value:
+dd 0x40400000 ; 3.0
+dd 0x40800000 ; 4.0