tests/fixedbugs: regression test for issue 100 (#129)

Adds a regression test based on klauspost/compress#186. This necessitated some related changes:

* Mark "RET" as a terminal instruction
* printer refactor to maintain compatibility with asmfmt
* Tweaks to other regression tests to ensure they are run correctly in CI

Updates #100 #65 #8

printer/goasm_test.go

@@ -81,3 +81,27 @@ func TestConstraints(t *testing.T) {
 		"",
 	})
 }
+
+func TestAlignmentNoOperands(t *testing.T) {
+	ctx := build.NewContext()
+	ctx.Function("alignment")
+	ctx.SignatureExpr("func()")
+	ctx.ADDQ(reg.RAX, reg.RBX)
+	ctx.VMOVDQU(reg.Y4, reg.Y11)
+	ctx.VZEROUPPER()
+	ctx.ADDQ(reg.R9, reg.R13)
+	ctx.RET()
+
+	AssertPrintsLines(t, ctx, printer.NewGoAsm, []string{
+		"// Code generated by avo. DO NOT EDIT.",
+		"",
+		"// func alignment()",
+		"TEXT ·alignment(SB), $0",
+		"\tADDQ    AX, BX",
+		"\tVMOVDQU Y4, Y11",
+		"\tVZEROUPPER",      // instruction with no alignment doesn't affect width
+		"\tADDQ    R9, R13", // retains alignment from above
+		"\tRET",
+		"",
+	})
+}