build: turn on -Wundef

Protects against typos in #if. For instance, the following would
silently disable the code block because of the typo:

    #if HAVE_LIBDRN
    name = drmGetFormatName(format);
    #endif

Signed-off-by: Simon Ser <contact@emersion.fr>

meson.build

@@ -18,8 +18,10 @@ dir_inc = include_directories('.')
 pkgconfig = import('pkgconfig')
 
 cc = meson.get_compiler('c')
-cflags = ['-Wno-unused-parameter']
-add_project_arguments(cflags, language: 'c')
+add_project_arguments(cc.get_supported_arguments([
+	'-Wundef',
+	'-Wno-unused-parameter',
+]), language: 'c')
 
 dep_wayland_client = dependency('wayland-client', version: '>= 1.20.0')
 dep_libdrm = dependency('libdrm', version: '>=2.4.107', required: get_option('drm'))