Silence warnings when testing gccs

This silences the warning that gcc-4.2 produces on Yosemite:

    couldn't understand kern.osversion `14.0.0'

bin/ruby-build

@@ -766,7 +766,7 @@ verify_gcc() {
     return 1
   fi
 
-  local version="$("$gcc" --version || true)"
+  local version="$("$gcc" --version 2>/dev/null || true)"
   if [ -z "$version" ]; then
     return 1
   fi

test/compiler.bats

@@ -36,3 +36,13 @@ CC=${TMP}/bin/gcc
 MACOSX_DEPLOYMENT_TARGET=10.9
 OUT
 }
+
+@test "require_gcc silences warnings" {
+  stub gcc '--version : echo warning >&2; echo 4.2.1'
+
+  run_inline_definition <<DEF
+require_gcc
+echo \$CC
+DEF
+  assert_success "${TMP}/bin/gcc"
+}