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

tests/fixedbugs/issue100/minrepro/minrepro_test.go

@@ -0,0 +1,15 @@
+package minrepro
+
+import (
+	"testing"
+)
+
+//go:generate go run asm.go -out minrepro.s -stubs stub.go
+
+func TestIssue100(t *testing.T) {
+	n := uint64(100)
+	expect := n * (n + 1) / 2
+	if got := Issue100(); got != expect {
+		t.Fatalf("Issue100() = %v; expect %v", got, expect)
+	}
+}