Unbreak build when building without GMP support.

Add support for a new preprocessor macro EMACS_MODULE_HAVE_MPZ_T to
emacs-module.h.  If this macro is defined, assume that mpz_t is
already defined and don’t include gmp.h.

Don’t document the new macro for now, as it’s unclear whether we want
to support this in modules outside the Emacs tree.

* src/emacs-module.h.in: Allow user to prevent inclusion of gmp.h.

* src/emacs-module.c: Use mini-gmp if GMP is unavailable.  Don’t
include gmp.h.

* src/lisp.h: Don’t require gmp.h.  It’s not needed for lisp.h.

* test/Makefile.in (GMP_LIB, GMP_OBJ): New variables.
($(test_module)): Use them.

* test/data/emacs-module/mod-test.c: Use mini-gmp if GMP is unavailable.

src/emacs-module.c

@@ -70,6 +70,11 @@ To add a new module function, proceed as follows:
 
 #include <config.h>
 
+#ifndef HAVE_GMP
+#include "mini-gmp.h"
+#define EMACS_MODULE_HAVE_MPZ_T
+#endif
+
 #define EMACS_MODULE_GMP
 #include "emacs-module.h"
 
@@ -80,8 +85,6 @@ To add a new module function, proceed as follows:
 #include <stdlib.h>
 #include <time.h>
 
-#include <gmp.h>
-
 #include "lisp.h"
 #include "bignum.h"
 #include "dynlib.h"

src/emacs-module.h.in

@@ -28,7 +28,7 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #include <stdbool.h>
 #endif
 
-#ifdef EMACS_MODULE_GMP
+#if defined EMACS_MODULE_GMP && !defined EMACS_MODULE_HAVE_MPZ_T
 #include <gmp.h>
 #endif
 

test/Makefile.in

@@ -257,6 +257,7 @@ endif
 HYBRID_MALLOC = @HYBRID_MALLOC@
 LIBEGNU_ARCHIVE = ../lib/lib$(if $(HYBRID_MALLOC),e)gnu.a
 GMP_LIB = @GMP_LIB@
+GMP_OBJ = $(if @GMP_OBJ@, ../src/@GMP_OBJ@)
 
 # Note: emacs-module.h is generated from emacs-module.h.in, hence we
 # look in ../src, not $(srcdir)/../src.
@@ -269,7 +270,7 @@ src/emacs-module-tests.log: $(test_module)
 $(test_module): $(test_module:${SO}=.c) ../src/emacs-module.h $(LIBEGNU_ARCHIVE)
 	$(AM_V_at)${MKDIR_P} $(dir $@)
 	$(AM_V_CCLD)$(CC) -shared $(CPPFLAGS) $(MODULE_CFLAGS) $(LDFLAGS) \
-	  -o $@ $< $(LIBEGNU_ARCHIVE) $(GMP_LIB)
+	  -o $@ $< $(LIBEGNU_ARCHIVE) $(GMP_LIB) $(GMP_OBJ)
 endif
 
 ## Check that there is no 'automated' subdirectory, which would

test/data/emacs-module/mod-test.c

@@ -27,11 +27,16 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #include <string.h>
 #include <time.h>
 
+#ifdef HAVE_GMP
+#include <gmp.h>
+#else
+#include "mini-gmp.h"
+#define EMACS_MODULE_HAVE_MPZ_T
+#endif
+
 #define EMACS_MODULE_GMP
 #include <emacs-module.h>
 
-#include <gmp.h>
-
 #include "timespec.h"
 
 int plugin_is_GPL_compatible;