Using TS_ADDTO to add the custom locations of libraries results in incorrect "-rpath" directive to the linker. This is because TS_ADDTO creates a unique list of tokens that it adds to its target. E.g.,
./configure --with-openssl=/usr/local/openssl --with-zlib=/usr/local/zlib
the above should result in
LIBTOOL_LINK_FLAGS: -rpath /usr/local/openssl/lib /usr/local/zlib/lib
The absence of "-rpath" in front of the second path causes an error in the linker!
This is fixed by introducing a new macro TS_ADD_RPATH_TO that takes a path and adds it with the "-rpath " prefix.
Also added influential environmental variable RPATH that can be used to give a base value for the rpath. So, the following
./configure --with-openssl=/usr/local/openssl --with-zlib=/usr/local/zlib RPATH=/foo
will result in
LIBTOOL_LINK_FLAGS: -rpath /foo -rpath /usr/local/zlib/lib -rpath /usr/local/openssl/lib