[dev.cc] cmd/asm: final fixups for correct assembly of runtime, the last package to verify

- obj: add a missing setting of the context for a generated JMP instruction
- asm:  correct the encoding of mode (R)(R*scale)
- asm: fix a silly bug in the test for macro recursion.
- asm: accept address mode sym(R)(R*8); was an oversight

Change-Id: I27112eaaa1faa0d2ba97e414f0571b70733ea087
Reviewed-on: https://go-review.googlesource.com/4502
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/asm/internal/lex/input.go

@@ -93,9 +93,9 @@ func (in *Input) Next() ScanToken {
 		in.text = in.peekText
 		return tok
 	}
-	// If we cannot generate a token after 100 tries, we're in trouble.
+	// If we cannot generate a token after 100 macro invocations, we're in trouble.
 	// The usual case is caught by Push, below, but be safe.
-	for i := 0; i < 100; i++ {
+	for nesting := 0; nesting < 100; {
 		tok := in.Stack.Next()
 		switch tok {
 		case '#':
@@ -108,6 +108,7 @@ func (in *Input) Next() ScanToken {
 			name := in.Stack.Text()
 			macro := in.macros[name]
 			if macro != nil {
+				nesting++
 				in.invokeMacro(macro)
 				continue
 			}