[gnome-settings-daemon] build: Fix error when doing non-debug builds

[Bastien Nocera <hadess src gnome org>]

commit 94a5cc2c77a77ebc19d0de1a3b44d21809d7c34e
Author: Bastien Nocera <hadess hadess net>
Date:   Tue Feb 6 11:41:31 2018 +0100

    build: Fix error when doing non-debug builds
    
    compiler_flags needs to be defined both when doing debug builds (as it
    was) and non-debug builds to avoid an error.
    
    Spotted by Kalev Lember <klember redhat com>

 meson.build |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/meson.build b/meson.build
index 1fc2782..51fd03c 100644
--- a/meson.build
+++ b/meson.build
@@ -69,6 +69,7 @@ if get_option('buildtype').contains('debug')
   compiler_flags = cc.get_supported_arguments(test_cflags)
 else
   common_flags += ['-DG_DISABLE_CHECKS']
+  compiler_flags = []
 endif
 
 # Workaround for meson's bug