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/allocfail/stubs.go

@@ -0,0 +1,85 @@
+// Code generated by command: go run asm.go -out allocfail.s -stubs stubs.go. DO NOT EDIT.
+
+// +build !appengine
+// +build !noasm
+// +build gc
+
+package allocfail
+
+// encodeBlockAsm encodes a non-empty src to a guaranteed-large-enough dst.
+// It assumes that the varint-encoded length of the decompressed bytes has already been written.
+//
+//go:noescape
+func encodeBlockAsm(dst []byte, src []byte) int
+
+// encodeBlockAsm14B encodes a non-empty src to a guaranteed-large-enough dst.
+// It assumes that the varint-encoded length of the decompressed bytes has already been written.
+//
+//go:noescape
+func encodeBlockAsm14B(dst []byte, src []byte) int
+
+// encodeBlockAsm12B encodes a non-empty src to a guaranteed-large-enough dst.
+// It assumes that the varint-encoded length of the decompressed bytes has already been written.
+//
+//go:noescape
+func encodeBlockAsm12B(dst []byte, src []byte) int
+
+// encodeBlockAsmAvx encodes a non-empty src to a guaranteed-large-enough dst.
+// It assumes that the varint-encoded length of the decompressed bytes has already been written.
+//
+//go:noescape
+func encodeBlockAsmAvx(dst []byte, src []byte) int
+
+// encodeBlockAsm14BAvx encodes a non-empty src to a guaranteed-large-enough dst.
+// It assumes that the varint-encoded length of the decompressed bytes has already been written.
+//
+//go:noescape
+func encodeBlockAsm14BAvx(dst []byte, src []byte) int
+
+// encodeBlockAsm12BAvx encodes a non-empty src to a guaranteed-large-enough dst.
+// It assumes that the varint-encoded length of the decompressed bytes has already been written.
+//
+//go:noescape
+func encodeBlockAsm12BAvx(dst []byte, src []byte) int
+
+// emitLiteral writes a literal chunk and returns the number of bytes written.
+//
+// It assumes that:
+//   dst is long enough to hold the encoded bytes
+//   0 <= len(lit) && len(lit) <= math.MaxUint32
+//
+//go:noescape
+func emitLiteral(dst []byte, lit []byte) int
+
+// emitLiteralAvx writes a literal chunk and returns the number of bytes written.
+//
+// It assumes that:
+//   dst is long enough to hold the encoded bytes
+//   0 <= len(lit) && len(lit) <= math.MaxUint32
+//
+//go:noescape
+func emitLiteralAvx(dst []byte, lit []byte) int
+
+// emitRepeat writes a repeat chunk and returns the number of bytes written.
+// Length must be at least 4 and < 1<<32
+//
+//go:noescape
+func emitRepeat(dst []byte, offset int, length int) int
+
+// emitCopy writes a copy chunk and returns the number of bytes written.
+//
+// It assumes that:
+//   dst is long enough to hold the encoded bytes
+//   1 <= offset && offset <= math.MaxUint32
+//   4 <= length && length <= 1 << 24
+//
+//go:noescape
+func emitCopy(dst []byte, offset int, length int) int
+
+// matchLen returns how many bytes match in a and b
+//
+// It assumes that:
+//   len(a) <= len(b)
+//
+//go:noescape
+func matchLen(a []byte, b []byte) int