Rename "build_" to "compile_"

Recent versions of meson complain about an option having name starting
with "build_":

> DEPRECATION: Option uses prefix "build_", which is reserved for Meson.
> This will become an error in the future.

Use "compile_" instead.

meson.build

@@ -3,11 +3,11 @@ project('scrcpy', 'c',
         meson_version: '>= 0.37',
         default_options: 'c_std=c11')
 
-if get_option('build_app')
+if get_option('compile_app')
     subdir('app')
 endif
 
-if get_option('build_server')
+if get_option('compile_server')
     subdir('server')
 endif