meson: Really define _FORTIFY_SOURCE for optimised builds

Commit 965c5bf7fb ("meson: Define _FORTIFY_SOURCE for optimised
builds") tried to define _FORTIFY_SOURCE for optimised builds with
clang, but updated the common_arguments after it was used. This resulted
in the _FORTIFY_SOURCE option not being applied. Fix it.

Fixes: 965c5bf7fb ("meson: Define _FORTIFY_SOURCE for optimised builds")
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

meson.build

@@ -35,8 +35,8 @@ common_arguments = [
     '-include', 'config.h',
 ]
 
-c_arguments = common_arguments
-cpp_arguments = common_arguments
+c_arguments = []
+cpp_arguments = []
 
 if cc.get_id() == 'clang'
     # Turn _FORTIFY_SOURCE by default on optimised builds (as it requires -O1
@@ -56,6 +56,9 @@ if cc.get_id() == 'clang'
     endif
 endif
 
+c_arguments += common_arguments
+cpp_arguments += common_arguments
+
 add_project_arguments(c_arguments, language : 'c')
 add_project_arguments(cpp_arguments, language : 'cpp')
 add_project_link_arguments(cpp_arguments, language : 'cpp')