meson: enable -fno-common by default

This flag is enabled by default starting with gcc 10.
All the compilation issues have been fixed, so use it by default
to make sure we're not introducing regressions.

Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4058>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4058>
diff --git a/meson.build b/meson.build
index 1484e7f..bf30660 100644
--- a/meson.build
+++ b/meson.build
@@ -958,6 +958,7 @@
     '-fno-math-errno',
     '-fno-trapping-math',
     '-Qunused-arguments',
+    '-fno-common',
   ]
   # MinGW chokes on format specifiers and I can't get it all working
   if not (cc.get_id() == 'gcc' and host_machine.system() == 'windows')