Add ActiveGAPState() helper, use it in STATE macro

This allows implementing the STATE() macro uniformly for GAP and HPC-GAP.
ActiveGAPState() also provides a uniform way to access the active GAP state
when debugging the kernel with gdb or lldb.

src/debug.c

@@ -56,6 +56,7 @@ void InstallBacktraceHandlers(void) {
 // gdb or lldb.
 typedef void (* VoidFunc)(void);
 VoidFunc debug_func_pointers[] = {
+   (VoidFunc)ActiveGAPState,
    (VoidFunc)ADDR_OBJ,
    (VoidFunc)ADDR_PPERM2,
    (VoidFunc)ADDR_PPERM4,

src/gapstate.h

@@ -183,10 +183,16 @@ typedef struct GAPState {
 #else
 
 extern GAPState MainGAPState;
-#define STATE(x) (MainGAPState.x)
+
+static inline GAPState * ActiveGAPState(void)
+{
+    return &MainGAPState;
+}
 
 #endif
 
+#define STATE(x) (ActiveGAPState()->x)
+
 /* Access a module's registered state */
 #define MODULE_STATE(module, var) \
     (((module ## ModuleState *)(&STATE(StateSlots)[module ## StateOffset]))->var)

src/hpc/tls.h

@@ -83,7 +83,11 @@ static ALWAYS_INLINE ThreadLocalStorage *GetTLS(void)
 #endif /* HAVE_NATIVE_TLS */
 
 #define TLS(x) realTLS->x
-#define STATE(x) TLS(state).x
+
+static inline GAPState * ActiveGAPState(void)
+{
+    return &TLS(state);
+}
 
 static inline int IsMainThread(void)
 {