libgo patch committed: permit $AR to include options

[Ian Lance Taylor via Gcc-patches]

This libgo patch changes the go tool to permit the AR environment
variable to include options.  This mirrors the way it already handles
the CC environment variable.

This ports https://go.dev/cl/526275 to the gofrontend repo.

This is needed for gccgo testing because the top-level GCC Makefile
now passes a --plugin option to ar if it supports one.

Bootstrapped and ran Go testsuite on x86_64-pc-linux-gnu.  Committed
to mainline.

Ian

dab7163feedc99bd94549ee490031f86f8d0a6ca
diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE
index 83ab3e2d64c..30710e856cb 100644
--- a/gcc/go/gofrontend/MERGE
+++ b/gcc/go/gofrontend/MERGE
@@ -1,4 +1,4 @@
-d04b024021bb7dbaa434a6d902bd12beb08e315f
+53cdfab53ce79d8dfc1df01a696d4ffc43f17c3d
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.
diff --git a/libgo/go/cmd/go/internal/work/gccgo.go 
b/libgo/go/cmd/go/internal/work/gccgo.go
index c1026c71e01..3e07f8791eb 100644
--- a/libgo/go/cmd/go/internal/work/gccgo.go
+++ b/libgo/go/cmd/go/internal/work/gccgo.go
@@ -45,12 +45,8 @@ func (gccgoToolchain) linker() string {
        return GccgoBin
 }
 
-func (gccgoToolchain) ar() string {
-       ar := cfg.Getenv("AR")
-       if ar == "" {
-               ar = "ar"
-       }
-       return ar
+func (gccgoToolchain) ar() []string {
+       return envList("AR", "ar")
 }
 
 func checkGccgoBin() {