add solaris/SunOS cmake build support

Tested on a (physical) SunOS 5.10 SPARC machine
with 4 64 bit processors -> 16 cores :-)

SPARC is big-endian and our sha1.h needs to know.
This makes a config-cmake.h.in necessary.
Cmake creates a config.h like done by the autotools.

Cmake could add these defines in CMakeLists.txt,
but our code expects a config.h in that case.

Not setting endianness would compile fine,
but lead to ./test_discid failing 2 of 4 tests.
autotools, solaris: remove -lsocket and -lnsl

These libs were necessary for libmusicbrainz,
but we don't do any network communication.

Tested on that cool SunOS machine again.