Install include directory into includedir

Follow includedir parameter when installing include directory.

include/wlr/meson.build

@@ -9,5 +9,6 @@ version_data.set('WLR_VERSION_API_CURRENT',  so_version[0])
 version_data.set('WLR_VERSION_API_REVISION', so_version[1])
 version_data.set('WLR_VERSION_API_AGE',      so_version[2])
 
-configure_file(output: 'config.h',  install_dir: 'include/wlr', configuration: conf_data)
-configure_file(output: 'version.h', install_dir: 'include/wlr', configuration: version_data)
+wlr_inc_dest = join_paths(get_option('includedir'), 'wlr')
+configure_file(output: 'config.h',  install_dir: wlr_inc_dest, configuration: conf_data)
+configure_file(output: 'version.h', install_dir: wlr_inc_dest, configuration: version_data)

meson.build

@@ -125,8 +125,10 @@ if get_option('enable-xwayland')
 else
 	exclude_headers += 'xwayland.h'
 endif
+
+includedir = get_option('includedir')
 exclude_headers += 'meson.build'
-install_subdir('include/wlr', install_dir: 'include', exclude_files: exclude_headers)
+install_subdir('include/wlr', install_dir: includedir, exclude_files: exclude_headers)
 
 
 subdir('include')