insns.dat: add MOVSX -> CBW/CWDE/CDQE optimiztion; add MOVZX[D]

Add MOVSX[D] -> CBW/CWDE/CDQE optimization patterns when the suitable
form of the AX register are referenced.

Add MOVZX reg64,rm32 pattern which converts to a 32-bit MOV.

Add MOVZXD reg64,rm32 alias pattern for consistency.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

test/movszx.asm

@@ -0,0 +1,33 @@
+	bits 64
+
+	movsx ax,al
+	movsx eax,al
+	movsx eax,ax
+	movsx rax,al
+	movsx rax,ax
+	movsx rax,eax
+	movsxd rax,eax
+
+	movsx cx,cl
+	movsx ecx,cl
+	movsx ecx,cx
+	movsx rcx,cl
+	movsx rcx,cx
+	movsx rcx,ecx
+	movsxd rcx,ecx
+
+	movzx ax,al
+	movzx eax,al
+	movzx eax,ax
+	movzx rax,al
+	movzx rax,ax
+	movzx rax,eax
+	movzxd rax,eax
+
+	movzx cx,cl
+	movzx ecx,cl
+	movzx ecx,cx
+	movzx rcx,cl
+	movzx rcx,cx
+	movzx rcx,ecx
+	movzxd rcx,ecx