Changes by GROMACS to muparser files
====================================
Used from https://github.com/beltoforion/muparser/releases/tag/v2.3.4.

ENABLE_SAMPLES is set off

ENABLE_OPENMP gets its value from GMX_OPENMP

The minimum required CMake version was changed to match that used for
GROMACS, so that the policy usage is consistent, so that muParser
cache variables can be overridden by normal GROMACS variables without
causing warnings.

target_include_directories() is used so that GROMACS source files
find the muparser headers.
