Change module interface to no longer use GMP objects directly.
As described in the new comment added to emacs-module.c, using GMP directly in the module interface has significant downsides: it couples the module interface directly to the implementation and requires module authors to link their module against the same GMP library as Emacs itself, which is often difficult and an unnecessary burden. By picking a representation for the magnitude that often matches the one used by GMP, we can avoid overhead when converting from and to GMP in most cases. Loading the test module in test/data/emacs-module and evaluating (dotimes (_ 10000) (mod-test-double (* 2 most-negative-fixnum))) under Callgrind shows that on my (GNU/Linux) machine Emacs only spends 10% of the CPU time of mod-test-double in mpz_import and mpz_export combined, even though that function does little else. (By contrast, 30% is spent in allocate_pseudovector.) * src/emacs-module.h.in: Don't check EMACS_MODULE_GMP. Don't include gmp.h. Remove emacs_mpz structure. Instead, define type alias emacs_limb_t and macro EMACS_LIMB_MAX. * src/module-env-27.h: Change interface of extract_big_integer and make_big_integer to take a sign-magnitude representation instead of mpz_t. * src/emacs-module.c: Don't check EMACS_MODULE_GMP or EMACS_MODULE_HAVE_MPZ_T. Add a comment about the chosen implementation. (module_extract_big_integer, module_make_big_integer): Reimplement without using mpz_t in the interface. * doc/lispref/internals.texi (Module Values): Adapt function documentation and example. Stop mentioning GMP and EMACS_MODULE_GMP. * test/data/emacs-module/mod-test.c: Don't define EMACS_MODULE_GMP or EMACS_MODULE_HAVE_MPZ_T. (memory_full, extract_big_integer, make_big_integer): New helper functions, identical to example in the Info documentation. (Fmod_test_nanoseconds, Fmod_test_double): Adapt to new interface.