feature(iw5: gsc): use preprocessor to deduplicate code (#308)

GameFiles/GameInterface/_integration_utility.gsh

@@ -0,0 +1,40 @@
+/*
+* This file contains reusable preprocessor directives meant to be used on
+* Plutonium & AlterWare clients that are up to date with the latest version.
+* Older versions of Plutonium or other clients do not have support for loading
+* or parsing "gsh" files.
+*/
+
+/*
+* Turn off assertions by removing the following define
+* gsc-tool will only emit assertions if developer_script dvar is set to 1
+* In short, you should not need to remove this define. Just turn them off
+* by using the dvar
+*/
+
+#define _INTEGRATION_DEBUG
+
+#ifdef _INTEGRATION_DEBUG
+
+#define _VERIFY( cond, msg ) \
+    assertEx( cond, msg )
+
+#else
+
+// This works as an "empty" define here with gsc-tool
+#define _VERIFY( cond, msg )
+
+#endif
+
+// This function is meant to be used inside "client commands"
+// If the client is not alive it shall return an error message
+#define _IS_ALIVE( ent ) \
+    _VERIFY( ent, "player entity is not defined" ); \
+    if ( !IsAlive( ent ) ) \
+    { \
+        return ent.name + "^7 is not alive"; \
+    }
+
+// This function should be used to verify if a player entity is defined
+#define _VERIFY_PLAYER_ENT( ent ) \
+    _VERIFY( ent, "player entity is not defined" )