build: fix ordering problems with lib-provided and internal RPATHs

build: fix ordering problems with lib-provided and internal RPATHs

When a library or system (like cups) provides an RPATH,
e.g. with -Wl,-R or -Wl,-rpath, this was added by waf
to the LINKFLAGS, wich was later prepended to our RPATH.
But if the path by chance contains an older version of
one of our internal libraries like talloc, this would lead
to linking the too old talloc into our binaries.

This has been observed on, e.g., FreeBSD, but it is a general
problem.

This patch fixes the problem by specially parsing the RPATH
linker options from the pkg-config(, cups-config, ....) output
and putting the paths into the RPATH_<lib> container, which
is then later correctly appended to our internal RPATH.

Signed-off-by: Michael Adam <obnox@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>