fix LD_LIBRARY_PATH in makefiles to not use semicolon

The current makefiles generate invalid LD_LIBRARY_PATHs like:

    LD_LIBRARY_PATH="../alib2std/lib-release;../alib2common/lib-release;lib-release" test-bin-release/alib2test

Standard directory separator on Unix/Linux systems is a colon. I found
that semicolon may be used to separate two lists of directories - the
first one is searched before the list(s) supplied on the command line,
the second one is searched after. But that's apparently not the case
here.

It seems that glibc doesn't care about it, because it somehow works on
Jenkins that runs on Gentoo. However, more correct libc libraries, like
musl libc, do care about it and don't accept such LD_LIBRARY_PATH.