premake: support structuredAttrs in setup hook

Tested gmad with and without __structuredAttrs.

Building it succeeded on master with structuredAttrs, but the log output
showed that the configure flags were not passed correctly previously.

pkgs/development/tools/misc/premake/setup-hook.sh

@@ -3,9 +3,8 @@ premakeConfigurePhase() {
 
     local flagsArray=(
         ${premakefile:+--file=$premakefile}
-        $premakeFlags ${premakeFlagsArray[@]}
-        ${premakeBackend:-gmake}
     )
+    concatTo flagsArray premakeFlags premakeFlagsArray premakeBackend=gmake
 
     echoCmd 'configure flags' "${flagsArray[@]}"