cmd/cgo/internal/testshared: strip newline from gccgo -dumpversion

Otherwise, gccgo tests may be quietly skipped.

For #60798

Change-Id: Iaad6b53c95ad4d407b917d8f62978979b82a4e81
Reviewed-on: https://go-review.googlesource.com/c/go/+/503495
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
Run-TryBot: Paul Murphy <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: pmur

src/cmd/cgo/internal/testshared/shared_test.go

@@ -748,7 +748,7 @@ func requireGccgo(t *testing.T) {
 	if dot > 0 {
 		output = output[:dot]
 	}
-	major, err := strconv.Atoi(string(output))
+	major, err := strconv.Atoi(strings.TrimSpace(string(output)))
 	if err != nil {
 		t.Skipf("can't parse gccgo version number %s", output)
 	}