cmd/dist,cmd/compile: remove -allabis mode

dist passes the -allabis flag to the compiler to avoid having to
recreate the cross-package ABI logic from cmd/go. However, we removed
that logic from cmd/go in CL 179863 and replaced it with a different
mechanism that doesn't depend on the build system. Hence, passing
-allabis in dist is no longer necessary.

This CL removes -allabis from dist and, since that was the only use of
it, removes support for it from the compiler as well.

Updates #31230.

Change-Id: Ib005db95755a7028f49c885785e72c3970aea4f9
Reviewed-on: https://go-review.googlesource.com/c/go/+/181079
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

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

@@ -259,7 +259,6 @@ func Main(archInit func(*Arch)) {
 	flag.StringVar(&goversion, "goversion", "", "required version of the runtime")
 	var symabisPath string
 	flag.StringVar(&symabisPath, "symabis", "", "read symbol ABIs from `file`")
-	flag.BoolVar(&allABIs, "allabis", false, "generate ABI wrappers for all symbols (for bootstrap)")
 	flag.StringVar(&traceprofile, "traceprofile", "", "write an execution trace to `file`")
 	flag.StringVar(&blockprofile, "blockprofile", "", "write block profile to `file`")
 	flag.StringVar(&mutexprofile, "mutexprofile", "", "write mutex profile to `file`")
@@ -849,11 +848,6 @@ func readImportCfg(file string) {
 // name, where the local package prefix is always `"".`
 var symabiDefs, symabiRefs map[string]obj.ABI
 
-// allABIs indicates that all symbol definitions should have ABI
-// wrappers. This is used during toolchain bootstrapping to avoid
-// having to find cross-package references.
-var allABIs bool
-
 // readSymABIs reads a symabis file that specifies definitions and
 // references of text symbols by ABI.
 //