Add support for Meson as alternative/parallel build system

https://github.com/mesonbuild/meson

With contributions from:

Tim-Philipp Müller <tim@centricular.com>
Jussi Pakkanen <jpakkane@gmail.com> (original port)

Highlights of the features provided are:
* Faster builds on Linux (~40-50% faster)
* The ability to build with MSVC on Windows
* Generate Visual Studio project files
* Generate XCode project files
* Much faster builds on Windows (on-par with Linux)
* Seriously fast configure and building on embedded

... and many more. For more details see:

http://blog.nirbheek.in/2016/05/gstreamer-and-meson-new-hope.html
http://blog.nirbheek.in/2016/07/building-and-developing-gstreamer-using.html

Building with Meson should work on both Linux and Windows, but may
need a few more tweaks on other operating systems.
diff --git a/gst-libs/gst/audio/audio_mkenum.py b/gst-libs/gst/audio/audio_mkenum.py
new file mode 100755
index 0000000..b3572de
--- /dev/null
+++ b/gst-libs/gst/audio/audio_mkenum.py
@@ -0,0 +1,55 @@
+#!/usr/bin/env python3
+
+# This is in its own file rather than inside meson.build
+# because a) mixing the two is ugly and b) trying to
+# make special characters such as \n go through all
+# backends is a fool's errand.
+
+import sys, os, shutil, subprocess
+
+h_array = ['--fhead',
+           "#ifndef __GST_AUDIO_ENUM_TYPES_H__\n#define __GST_AUDIO_ENUM_TYPES_H__\n\n#include <glib-object.h>\n\nG_BEGIN_DECLS\n",
+           '--fprod',
+           "\n/* enumerations from \"@filename@\" */\n",
+           '--vhead',
+           'GType @enum_name@_get_type (void);\n#define GST_TYPE_@ENUMSHORT@ (@enum_name@_get_type())\n',
+           '--ftail',
+           'G_END_DECLS\n\n#endif /* __GST_AUDIO_ENUM_TYPES_H__ */',
+           ]
+
+c_array = ['--fhead',
+           "#include \"audio-enumtypes.h\"\n\n#include \"audio.h\" \n#include \"audio-format.h\" \n#include \"audio-channels.h\" \n#include \"audio-info.h\" \n#include \"gstaudioringbuffer.h\"",
+           '--fprod',
+           "\n/* enumerations from \"@filename@\" */",
+           '--vhead',
+           "GType\n@enum_name@_get_type (void)\n{\n  static volatile gsize g_define_type_id__volatile = 0;\n  if (g_once_init_enter (&g_define_type_id__volatile)) {\n    static const G@Type@Value values[] = {",
+           '--vprod',
+           "      { @VALUENAME@, \"@VALUENAME@\", \"@valuenick@\" },",
+           '--vtail',
+           "      { 0, NULL, NULL }\n    };\n    GType g_define_type_id = g_@type@_register_static (\"@EnumName@\", values);\n    g_once_init_leave (&g_define_type_id__volatile, g_define_type_id);\n  }\n  return g_define_type_id__volatile;\n}\n",
+           ]
+
+cmd = []
+argn = 1
+# Find the full command needed to run glib-mkenums
+# On UNIX-like, this is just the full path to glib-mkenums
+# On Windows, this is the full path to interpreter + full path to glib-mkenums
+for arg in sys.argv[1:]:
+    cmd.append(arg)
+    argn += 1
+    if arg.endswith('glib-mkenums'):
+        break
+ofilename = sys.argv[argn]
+headers = sys.argv[argn + 1:]
+
+if ofilename.endswith('.h'):
+    arg_array = h_array
+else:
+    arg_array = c_array
+
+cmd_array = cmd + arg_array + headers
+pc = subprocess.Popen(cmd_array, stdout=subprocess.PIPE)
+(stdo, _) = pc.communicate()
+if pc.returncode != 0:
+    sys.exit(pc.returncode)
+open(ofilename, 'wb').write(stdo)