[gforth] GNU libffcall 2.0 is released

[Bruno Haible]

FYI, since gforth depends on libffcall:

Available at
  https://ftp.gnu.org/gnu/libffcall/libffcall-2.0.tar.gz

New in 2.0:

* The package now installs a library libffcall.{a,so}. It contains the
  'avcall' and 'callback' packages. The libraries libavcall.{a,so} and
  libcallback.{a,so} are still installed as well, but are deprecated.

* The installed libraries are now installed as shared libraries by default
  (except for libvacall, which is still a static library only).

* The installed shared libraries are now properly versioned. This means that
  when installing with --enable-shared, upgrading to a newer version of
  libffcall will not break existing binaries.

* The installed include files are now platform independent. This means that
  you can now install libffcall for different ABIs on the same system, using
  the same --prefix option but different --exec-prefix options for each ABI.

* API changes in <trampoline.h>:
  - The second argument of alloc_trampoline() is now a 'void**', rather
    than a 'void*'.
  - The return value of trampoline_variable() is now a 'void**', rather
    than a 'void*'.
  - The argument of trampoline_address(), trampoline_variable(),
    trampoline_data() is now a function pointer instead of a 'void*'.

* Fixed a bug regarding floating-point arguments followed by
  non-floating-point arguments on the following platforms:
  - arm: Linux 32-bit, with hardware floats.
  - powerpc: Linux 32-bit.
  - s390: Linux.

* Fixed a bug regarding structure returns on the following platforms:
  - i386: FreeBSD.
  - i386: MinGW.
  - mips: old 32-bit ABI (Linux, IRIX).

* Added support for the following platforms:
  (Previously, a build on these platforms failed.)
  - i386: MSVC 14.
  - x86_64: Cygwin.
  - x86_64: MinGW.
  - x86_64: MSVC 14.
  - hppa64: HP-UX 11.
  - m68k: Linux.

Bruno