Move common assembly into a separate file

injector/launcher_payload/meson.build

@@ -1,5 +1,8 @@
 # Assemble the payload that will be injected into the game
-l_payload_bin = asm_gen.process('src/payload.asm')
+l_payload_bin = asm_gen.process(
+    'src/payload.asm',
+    extra_args: [ str_include_dir ]
+)
 
 # Embed it into the library
 l_res_files = custom_target(
@@ -13,6 +16,6 @@ shared_library(
     'launcher_payload',
     'src/dll.c',
     l_res_files,
-    include_directories: '../include',
+    include_directories: include_dir,
     name_prefix: ''
 )