Skip testing --enable-all in MinGW for now

If we don't intend to support this platform, we should probably enable
MJIT for MinGW. However, since the code for https://bugs.ruby-lang.org/issues/18439
is in place, I'm adjusting the test for it in the meantime.

following up https://github.com/ruby/ruby/pull/5363

spec/ruby/command_line/feature_spec.rb

@@ -43,7 +43,9 @@ describe "The --enable and --disable flags" do
     ruby_exe("p 'foo'.frozen?", options: "--disable-frozen-string-literal").chomp.should == "false"
   end
 
-  platform_is_not :darwin do # frequently hangs for >60s on GitHub Actions macos-latest
+  # frequently hangs for >60s on GitHub Actions macos-latest
+  # MinGW's YJIT support seems broken
+  platform_is_not :darwin, :mingw do
     it "can be used with all for enable" do
       e = "p [defined?(Gem), defined?(DidYouMean), $VERBOSE, 'foo'.frozen?]"
       env = {'RUBYOPT' => '-w'}