Fix SDL_mixer header installation after #9983 (#10021)

Also add basic sdl2_mixer test outside of browser tests that just
tests for successful compilation.

Fixes #10015

Author: sbc100

tests/sdl2_mixer.c

@@ -15,7 +15,9 @@ void sound_loop_then_quit() {
 
     emscripten_cancel_main_loop();
     printf("Shutting down\n");
+#ifdef REPORT_RESULT
     REPORT_RESULT(1);
+#endif
 }
 
 int main(int argc, char* argv[]){

tests/test_other.py

@@ -1803,6 +1803,9 @@ def test_sdl_endianness(self):
     run_process([PYTHON, EMCC, 'main.cpp'])
     self.assertContained('1234, 1234, 4321\n', run_js('a.out.js'))
 
+  def test_sdl2_mixer(self):
+    Building.emcc(path_from_root('tests', 'sdl2_mixer.c'), ['-s', 'USE_SDL_MIXER=2'], output_filename='a.out.js')
+
   def test_libpng(self):
     shutil.copyfile(path_from_root('tests', 'pngtest.png'), 'pngtest.png')
     Building.emcc(path_from_root('tests', 'pngtest.c'), ['--embed-file', 'pngtest.png', '-s', 'USE_ZLIB=1', '-s', 'USE_LIBPNG=1'], output_filename='a.out.js')

tools/ports/sdl2_mixer.py

@@ -37,11 +37,7 @@ def create():
                      ['external', 'native_midi', 'timidity'])
 
     # copy header to a location so it can be used as 'SDL2/'
-    dest_include_path = os.path.join(dest_path, 'include', 'SDL2')
-    os.makedirs(dest_include_path)
-    shutil.copyfile(os.path.join(source_path, 'SDL_mixer.h'),
-                    os.path.join(dest_include_path, 'SDL_mixer.h'))
-
+    ports.install_headers(source_path, pattern='SDL_*.h', target='SDL2')
     return final
 
   return [shared.Cache.get(libname, create, what='port')]

tools/system_libs.py

@@ -1553,8 +1553,10 @@ def install_headers(src_dir, pattern="*.h", target=None):
     if target:
       dest = os.path.join(dest, target)
       shared.safe_ensure_dirs(dest)
-    for f in glob.glob(os.path.join(src_dir, pattern)):
-      logger.debug(os.path.join(dest, os.path.basename(f)))
+    matches = glob.glob(os.path.join(src_dir, pattern))
+    assert matches, "no headers found to install in %s" % src_dir
+    for f in matches:
+      logger.debug('installing: ' + os.path.join(dest, os.path.basename(f)))
       shutil.copyfile(f, os.path.join(dest, os.path.basename(f)))
 
   @staticmethod