[tlbuild] dynamic libraries

[Martin Schröder]

> ldd inst/bin/x86_64-unknown-linux-gnu/xetex
        libfontconfig.so.1 => /usr/lib64/libfontconfig.so.1 (0x00002ac646c8d000)
        libfreetype.so.6 => /usr/lib64/libfreetype.so.6 (0x00002ac646ec2000)
        libz.so.1 => /lib64/libz.so.1 (0x00002ac647143000)
        libexpat.so.1 => /lib64/libexpat.so.1 (0x00002ac647359000)
        libm.so.6 => /lib64/libm.so.6 (0x00002ac64757d000)
        libc.so.6 => /lib64/libc.so.6 (0x00002ac6477d0000)
        /lib64/ld-linux-x86-64.so.2 (0x00002ac646a70000)

Do we really want libz and libexpat do be non-static?

Best
    Martin