make gobuild failures more readable.

make gobuild failures more readable.

1. ar reports names of objects with duplicate text symbols.
2. gobuild only shows first line of error output for each failed command.
3. gobuild ignores files that begin with ascii non-alphanumeric non _.

; gobuild
$ 6g -I _obj gobuild.go
  gobuild.go:150: PackageImports: undefined
$ 6g -I _obj makefile.go
  makefile.go:102: ShellString: undefined
$ 6g -I _obj util.go
  util.go:114: syntax error near zzz
gobuild: stalemate
;

; gobuild
$ 6ar grc _obj/gobuild.a util.6 util1.6
  duplicate text symbol: util1.6 and util.6: gobuild·Build
$ 6g -I _obj gobuild.go
  gobuild.go:150: PackageImports: undefined
$ 6g -I _obj makefile.go
  makefile.go:102: ShellString: undefined
gobuild: stalemate
;

R=r
DELTA=95  (49 added, 9 deleted, 37 changed)
OCL=29625
CL=29640