-rpath wont work when targeting Mac OS X 10.3 on 10.5

[sevan]

Fixes build on Leopard 10.5 where the use of -rpath fails with
ld: -rpath can only be used when targetting Mac OS X 10.5 or later.
Attempting to set MACOSX_DEPLOYMENT_TARGET is ignored.
We leave it set for 10.4 & prior as the linker would default to a deployment target of 10.1 on powerpc & 10.4 on intel builds and there's no issue with this on 10.4 currently.

[tonycoz]

The documentation for MACOSX_DEPLOYMENT_TARGET's effects are unfortunately poor :(

I couldn't find anything where perl adds -rpath on darwin based on MACOSX_DEPLOYMENT_TARGET*, so I assume the MACOSX_DEPLOYMENT_TARGET setting is making the toolchain use -rpath internally, causing the failure (let me know if I missed it).

* EU::MM uses it based on $Config{osvers}, but not MACOSX_DEPLOYMENT_TARGET

[sevan]

The documentation for MACOSX_DEPLOYMENT_TARGET's effects are unfortunately poor :(

I couldn't find anything where perl adds -rpath on darwin based on MACOSX_DEPLOYMENT_TARGET*, so I assume the MACOSX_DEPLOYMENT_TARGET setting is making the toolchain use -rpath internally, causing the failure (let me know if I missed it).

The compiler toolchain will default to using -rpath on 10.5 but having MACOSX_DEPLOYMENT_TARGET set to 10.3 prevents it from being used, so we raise MACOSX_DEPLOYMENT_TARGET in Perl since that's where the 10.3 setting originates from, rather than attempting to adapt the things so -rpath is not used (I haven't attempted it & unsure if it's possible).