scripts/gdb: fix usage of MOD_TEXT not defined when CONFIG_MODULES=n

MOD_TEXT is only defined if CONFIG_MODULES=y which lead to loading failure
of the gdb scripts when kernel is built without CONFIG_MODULES=y:

Reading symbols from vmlinux...
Traceback (most recent call last):
  File "/foo/vmlinux-gdb.py", line 25, in <module>
    import linux.constants
  File "/foo/scripts/gdb/linux/constants.py", line 14, in <module>
    LX_MOD_TEXT = gdb.parse_and_eval("MOD_TEXT")
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
gdb.error: No symbol "MOD_TEXT" in current context.

Add a conditional check on CONFIG_MODULES to fix this error.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: b4aff75 ("scripts/gdb: use mem instead of core_layout to get the module address")
Signed-off-by: Clément Léger <[email protected]>
Tested-by: Daniel Gomez <[email protected]>
Signed-off-by: Daniel Gomez <[email protected]>
Cc: Jan Kiszka <[email protected]>
Cc: Kieran Bingham <[email protected]>
Cc: Luis Chamberlain <[email protected]>
Cc: Pankaj Raghav <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: clementleger

scripts/gdb/linux/constants.py.in

@@ -66,10 +66,11 @@ LX_GDBPARSED(IRQD_LEVEL)
 LX_GDBPARSED(IRQ_HIDDEN)
 
 /* linux/module.h */
-LX_GDBPARSED(MOD_TEXT)
-LX_GDBPARSED(MOD_DATA)
-LX_GDBPARSED(MOD_RODATA)
-LX_GDBPARSED(MOD_RO_AFTER_INIT)
+if IS_BUILTIN(CONFIG_MODULES):
+    LX_GDBPARSED(MOD_TEXT)
+    LX_GDBPARSED(MOD_DATA)
+    LX_GDBPARSED(MOD_RODATA)
+    LX_GDBPARSED(MOD_RO_AFTER_INIT)
 
 /* linux/mount.h */
 LX_VALUE(MNT_NOSUID)