[gnome-system-monitor] Use warning level instead of -Wall flag

[Robert Roth <robertroth src gnome org>]

commit 083443e9729b33e22335a0bbb365c5c6e7dcc5fb
Author: Robert Roth <robert roth off gmail com>
Date:   Fri Aug 7 10:20:18 2020 +0300

    Use warning level instead of -Wall flag

 meson.build | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)
---
diff --git a/meson.build b/meson.build
index 272b248f..502bdb4a 100644
--- a/meson.build
+++ b/meson.build
@@ -2,7 +2,7 @@
 project('gnome-system-monitor',
   'c', 'cpp',
   default_options : [
-    'c_std=c11', 'cpp_std=c++11'
+    'c_std=c11', 'cpp_std=c++11', 'warning_level=3'
   ],
   version: '3.37.90',
   meson_version: '>=0.50.0',
@@ -69,7 +69,6 @@ conf.set('HAVE_SYSTEMD', libsystemd.found())
 # Compiler flags
 
 extra_flags = [
-  '-Wall',
   '-Wcast-align',
   '-Wchar-subscripts',
   '-Winline',