cmd/compile, cmd/link: create from 5g, 5l, etc

Trivial merging of 5g, 6g, ... into go tool compile,
and similarlly 5l, 6l, ... into go tool link.
The files compile/main.go and link/main.go are new.
Everything else in those directories is a move followed by
change of imports and package name.

This CL breaks the build. Manual fixups are in the next CL.

See golang-dev thread titled "go tool compile, etc" for background.

Change-Id: Id35ff5a5859ad9037c61275d637b1bd51df6828b
Reviewed-on: https://go-review.googlesource.com/10287
Reviewed-by: Dave Cheney <dave@cheney.net>
Reviewed-by: Rob Pike <r@golang.org>

src/cmd/compile/internal/gc/util.go

@@ -0,0 +1,103 @@
+package gc
+
+import (
+	"os"
+	"runtime"
+	"runtime/pprof"
+	"strconv"
+	"strings"
+)
+
+func (n *Node) Line() string {
+	return Ctxt.LineHist.LineString(int(n.Lineno))
+}
+
+func atoi(s string) int {
+	// NOTE: Not strconv.Atoi, accepts hex and octal prefixes.
+	n, _ := strconv.ParseInt(s, 0, 0)
+	return int(n)
+}
+
+func isalnum(c int) bool {
+	return isalpha(c) || isdigit(c)
+}
+
+func isalpha(c int) bool {
+	return 'A' <= c && c <= 'Z' || 'a' <= c && c <= 'z'
+}
+
+func isdigit(c int) bool {
+	return '0' <= c && c <= '9'
+}
+
+func plan9quote(s string) string {
+	if s == "" {
+		return "'" + strings.Replace(s, "'", "''", -1) + "'"
+	}
+	for i := 0; i < len(s); i++ {
+		if s[i] <= ' ' || s[i] == '\'' {
+			return "'" + strings.Replace(s, "'", "''", -1) + "'"
+		}
+	}
+	return s
+}
+
+// strings.Compare, introduced in Go 1.5.
+func stringsCompare(a, b string) int {
+	if a == b {
+		return 0
+	}
+	if a < b {
+		return -1
+	}
+	return +1
+}
+
+var atExitFuncs []func()
+
+func AtExit(f func()) {
+	atExitFuncs = append(atExitFuncs, f)
+}
+
+func Exit(code int) {
+	for i := len(atExitFuncs) - 1; i >= 0; i-- {
+		f := atExitFuncs[i]
+		atExitFuncs = atExitFuncs[:i]
+		f()
+	}
+	os.Exit(code)
+}
+
+var (
+	cpuprofile     string
+	memprofile     string
+	memprofilerate int64
+)
+
+func startProfile() {
+	if cpuprofile != "" {
+		f, err := os.Create(cpuprofile)
+		if err != nil {
+			Fatal("%v", err)
+		}
+		if err := pprof.StartCPUProfile(f); err != nil {
+			Fatal("%v", err)
+		}
+		AtExit(pprof.StopCPUProfile)
+	}
+	if memprofile != "" {
+		if memprofilerate != 0 {
+			runtime.MemProfileRate = int(memprofilerate)
+		}
+		f, err := os.Create(memprofile)
+		if err != nil {
+			Fatal("%v", err)
+		}
+		AtExit(func() {
+			runtime.GC() // profile all outstanding allocations
+			if err := pprof.WriteHeapProfile(f); err != nil {
+				Fatal("%v", err)
+			}
+		})
+	}
+}