Add dynamic module module support

* configure.ac: Add '--with-modules' option.  Conditionally add
  dynlib.o and module.o to the list of objects.  Add any system
  specific flags to the linker flags to support dynamic libraries.
* m4/ax_gcc_var_attribute.m4: Add autoconf extension to test gcc
  attributes.
* src/Makefile.in: Conditionally add module objects and linker flags.
* src/alloc.c (garbage_collect_1): protect module local values from
  GC.
* src/lisp.h: Add 'module_init' and 'syms_of_module' prototypes.
* src/emacs_module.h: New header file included by modules.  Public
  module API.
* src/module.c: New module implementation file.

Co-authored-by: Philipp Stephani <phst@google.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/alloc.c b/src/alloc.c
index 48ce3f120f5..53f974533a8 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -5574,6 +5574,10 @@ garbage_collect_1 (void *end)
   mark_fringe_data ();
 #endif
 
+#ifdef HAVE_MODULES
+  mark_modules ();
+#endif
+
   /* Everything is now marked, except for the data in font caches,
      undo lists, and finalizers.  The first two are compacted by
      removing an items which aren't reachable otherwise.  */