Log Message:
gammu: Do not set a LIB_SUFFIX in CMakeLists.txt

On some platforms (strictly speaking the ones that have libm
somewhere in a path with /lib64/) LIB_SUFFIX is set to `64' leading
to install phase/PLIST errors due libraries and pkg-config `.pc'
files are tried to be installed in `lib64/'.

Add a `cmakelists' SUBST_CLASS to avoid that.

This should fix problems noticed on Joyent CentOS 7.2/x86_64 bulk builds.