Fixing 'make check' due to Hans's "chg: StringAppend/StringSetS/StringEndS: use multiple times"
Replace --no-{rtti,exceptions} by -fno-{rtti,exceptions}

This improves compatibility with clang. Moreover, to the best
of my knowledge, the --no-* variants are undocumented to start with.
At least the GCC manuals for all versions from 2.95.3 till 4.7.2
only list the -fno-* variants, as far as I could tell.
Silence some warnings about statements without effect

Insired by [039a51b3aa3c77c2b7bae73d24de8521df45aed2]
Fix main() prototype of libparse

Conflicts:
	Singular/libparse.l
Fix spelling: "MacOS X" -> "Mac OS X"

The correct official spelling is indeed "Mac OS X". This is in
contrast to old macintosh operating systems which were called "MacOS"
as in "MacOS 7".

Conflicts:
	README
Due to Max Horn's "Include stddef.h before gmp.h"
Cleanup + fix libsingular-config