libgpg-error: Update to 1.20

libgpg-error: Update to 1.20

* configure.ac: Set LT version to C16/A16/R0.

Add new version macros.
* src/gpg-error.h.in (GPGRT_VERSION): New.
(GPGRT_VERSION_NUMBER): New.
(GPG_ERROR_VERSION, GPG_ERROR_VERSION_NUMBER): Move to top of file.

Add macro GPGRT_INLINE and avoid -Wundef warnings.
* src/gpg-error.h.in (GPG_ERR_INLINE): Use #if defined for possible
undefined macros to avoid warning with GCC's -Wundef option.
(GPGRT_INLINE): New.

Signed-off-by: Matthias Fischer <matthias.fischer@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>