package/mpdecimal: add optional C++ dependency

Version 2.5.0 enables the new libmpdec++ library by default:
http://www.bytereef.org/mpdecimal/changelog.html#version-2-5-0

Adapt the existing patch, to allow static build of this C++ library.

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
[yann.morin.1998@free.fr:
  - meld the C++-enabling and the static-patch commits into one
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
2 files changed