goversion: rewrite on top of cmd/go/internal/version

Imported the cmd/go/internal/version implementation at
c32140fa94cfc51a2152855825f57e27ae3ba133, and restored Symbols and
TextRange to implement the gccgo and crypto checks.

It looks like the amd64 matching had broken, but it should be more
stable to just track what we do upstream with minimal modifications, so
I replaced the core mechanism rather than fixing the matcher.

Fixes rsc#14
Fixes rsc#12
Fixes rsc#11
Fixes rsc#7
Closes rsc#13
Closes rsc#9

README.md

@@ -16,10 +16,10 @@ Goversion scans inside of tar or gzipped tar archives that it finds (named
 The `-crypto` flag causes goversion to print additional information about the
 crypto libraries linked into each executable.
 
-The -m flag causes goversion to print the list of modules
+The `-m` flag causes goversion to print the list of modules
 found in the executable, along with version information.
 
-The -mh flag causes goversion to print the list of modules
+The `-mh` flag causes goversion to print the list of modules
 found in the executable, along with version and hash information.
 
 The `-v` flag causes goversion to print information about every file it

go.mod

@@ -0,0 +1,3 @@
+module rsc.io/goversion
+
+go 1.14

main.go

@@ -71,10 +71,6 @@ var (
  verbose = flag.Bool("v", false, "print verbose information")
 )
 
-func init() {
- flag.BoolVar(&version.DebugMatch, "d", version.DebugMatch, "print debug information")
-}
-
 func usage() {
  fmt.Fprintf(os.Stderr, "usage: goversion [-crypto] [-v] path...\n")
  flag.PrintDefaults()