go/ssa: skip the "constraints" package in TestStdlib

go/ssa doesn't yet support generics, so the "constraints" package causes
this test to fail.

Updates golang/go#48595

Change-Id: I11c5a944bffba0c0398cd48ffca5d80fbede4332
Reviewed-on: https://go-review.googlesource.com/c/tools/+/352051
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

go/ssa/stdlib_test.go

@@ -51,7 +51,12 @@ func TestStdlib(t *testing.T) {
 	ctxt.GOPATH = ""      // disable GOPATH
 	conf := loader.Config{Build: &ctxt}
 	for _, path := range buildutil.AllPackages(conf.Build) {
-		conf.ImportWithTests(path)
+		// Temporarily skip packages that use generics until supported by go/ssa.
+		//
+		// TODO(#48595): revert this once go/ssa supports generics.
+		if !testenv.UsesGenerics(path) {
+			conf.ImportWithTests(path)
+		}
 	}
 
 	iprog, err := conf.Load()