gtk-demo: Speed up the build

Avoid serializing the gresource blob into a C string
and running gcc over it. Instead, use ld to put it
directly into an .o file and add it to the build.

The build system machinations here were copied from
gobject/tests/meson.build, and should ideally be part
of the meson gnome module.

demos/gtk-demo/meson.build

@@ -156,10 +156,69 @@ demos_h = custom_target('gtk4 demo header',
   command: [ find_program('geninclude.py'), '@OUTPUT@', '@INPUT@' ],
 )
 
-gtkdemo_resources = gnome.compile_resources('gtkdemo_resources',
-  'demo.gresource.xml',
-  source_dir: '.',
-)
+objcopy_supports_add_symbol = false
+objcopy = find_program('objcopy', required : false)
+if objcopy.found()
+  objcopy_supports_add_symbol = run_command(objcopy, '--help').stdout().contains('--add-symbol')
+endif
+
+ld = find_program('ld', required : false)
+
+if build_machine.system() == 'linux' and objcopy.found() and objcopy_supports_add_symbol and ld.found()
+  glib_compile_resources = find_program('glib-compile-resources')
+
+  # Create the resource blob
+  gtkdemo_gresource = custom_target('gtkdemo.gresource',
+      input : 'demo.gresource.xml',
+      output : 'gtkdemo.gresource',
+      command : [glib_compile_resources,
+                 '--target=@OUTPUT@',
+                 '--sourcedir=' + meson.current_source_dir(),
+                 '--sourcedir=' + meson.current_build_dir(),
+                 '@INPUT@'])
+
+  # Create resource data file
+  gtkdemo_resources_c = custom_target('gtkdemo_resources.c',
+      input : 'demo.gresource.xml',
+      output : 'gtkdemo_resources.c',
+      command : [glib_compile_resources,
+                 '--target=@OUTPUT@',
+                 '--sourcedir=' + meson.current_source_dir(),
+                 '--sourcedir=' + meson.current_build_dir(),
+                 '--generate-source',
+                 '--external-data',
+                 '--c-name', '_g_binary_gtkdemo',
+                 '@INPUT@'])
+
+  # Create object file containing resource data
+  gtkdemo_resources_binary = custom_target('gtkdemo_resources.o',
+      input : gtkdemo_gresource,
+      output : 'gtkdemo_resources.o',
+      command : [ld,
+                 '-r',
+                 '-b','binary',
+                 '@INPUT@',
+                 '-o','@OUTPUT@'])
+
+  # Rename symbol to match the one in the C file
+  gtkdemo_resources_o = custom_target('gtkdemo_resources2.o',
+    input : gtkdemo_resources_binary,
+    output : 'gtkdemo_resources2.o',
+    command : [objcopy,
+                 '--add-symbol','_g_binary_gtkdemo_resource_data=.data:0',
+                 '@INPUT@',
+                 '@OUTPUT@'])
+
+  gtkdemo_resources = [
+      gtkdemo_resources_c,
+      gtkdemo_resources_o,
+    ]
+else
+  gtkdemo_resources = gnome.compile_resources('gtkdemo_resources',
+    'demo.gresource.xml',
+    source_dir: '.',
+  )
+endif
 
 # Use a subset of compiler flags
 demo_cflags = []