x86asm: add support for FLDZ and FLDLN2

Fixes golang/go#18665.

Change-Id: Ia628773266d3e5efba252b910341d00b7fdb7081
GitHub-Last-Rev: fa98ffe
GitHub-Pull-Request: #3
Reviewed-on: https://go-review.googlesource.com/c/arch/+/149438
Run-TryBot: Cherry Zhang <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Cherry Zhang <[email protected]>

Author: mewmew

x86/x86.csv

@@ -484,7 +484,9 @@
 "FLDL2E","D9 EA","V","V","",""
 "FLDL2T","D9 E9","V","V","",""
 "FLDLG2","D9 EC","V","V","",""
+"FLDLN2","D9 ED","V","V","",""
 "FLDPI","D9 EB","V","V","",""
+"FLDZ","D9 EE","V","V","",""
 "FMUL ST(0), ST(i)","D8 C8+i","V","V","",""
 "FMUL ST(i), ST(0)","DC C8+i","V","V","",""
 "FMUL m32fp","D8 /1","V","V","",""

x86/x86asm/objdump_test.go

@@ -197,7 +197,6 @@ var unsupported = strings.Fields(`
 	clgi
 	femms
 	fldln
-	fldz
 	getsec
 	invlpga
 	kmov