component/librsync: compile in lib/ folder

Currently librsync is being compiled in the folder lib64 in some
OSes (e.g. SUSE SLE 15.6).
This is a problem because some dependents look for the library in the
lib subdirectory.
This change forces librsync to always use the lib directory.

See merge request nexedi/slapos!1629

component/librsync/buildout.cfg

@@ -18,6 +18,7 @@ configure-command = ${cmake:location}/bin/cmake
 configure-options =
   -DCMAKE_INSTALL_PREFIX=${:location}
   -DCMAKE_INSTALL_RPATH=${:location}/lib:${bzip2:location}/lib:${popt:location}/lib:${zlib:location}/lib
+  -DCMAKE_INSTALL_LIBDIR=lib
 make-options =
   VERBOSE=1
 environment =