makefiles/info-global.inc.mk: bug: fix DISABLE_MODULE_GLOBAL value

[cladmi]

Contribution description

The value must be saved from the original value to allow restoring it.

This has currently no impact as 'makefiles/defaultmodules.inc.mk'
and 'DISABLE_MODULE' are ignored in this parsing.

Testing procedure

With this diff applied:

diff --git a/makefiles/info-global.inc.mk b/makefiles/info-global.inc.mk
index 9e49a74a1..3189072b2 100644
--- a/makefiles/info-global.inc.mk
+++ b/makefiles/info-global.inc.mk
@@ -14,6 +14,7 @@ define board_missing_features
   DISABLE_MODULE    := $(DISABLE_MODULE_GLOBAL)
   FEATURES_REQUIRED := $(FEATURES_REQUIRED_GLOBAL)
   FEATURES_OPTIONAL := $(FEATURES_OPTIONAL_GLOBAL)
+  $$(warning DISABLE_MODULE == $$(DISABLE_MODULE))
 
   # Remove board specific variables set by Makefile.features/Makefile.dep
   FEATURES_PROVIDED :=

The value is now correct:

BOARDS=native make --no-print-directory -C tests/shell/ info-boards-supported
/home/harter/work/git/RIOT/makefiles/info-global.inc.mk:42: DISABLE_MODULE == auto_init
native

as it is the same as when compiling normally:

BOARD=native make --no-print-directory -C tests/shell/ info-debug-variable-DISABLE_MODULE
auto_init

Where in master it was empty:

BOARDS=native make --no-print-directory -C tests/shell/ info-boards-supported
/home/harter/work/git/RIOT/makefiles/info-global.inc.mk:42: DISABLE_MODULE == 
native

Issues/PRs references

Contribution in the context of #11477 while debugging with the output of #12004

[jcarrano]

Ok.

[cladmi]

Thank you for the review.