darwin.jam should not assume the same SDK and deployment target

[ippei_ukai@…]

First of all thank you for supporting SDK/deployment target in boost 1.35.

Unfortunately, however, the current implementation assumes that the SDK version and the macosx-version-min always match, which is wrong. Often deployment target is set below the SDK target, and the assumption made by the darwin.jam can cause a problem (I had to set those values of my project to match for now as a workaround). The better proper solution is to have separate option for SDK path and deployment target values.

Also, may need attention is the default values which are used in case those values are not specified. It is normal not to use the SDK but to link against the local installation itself when SDK is not specified. Also the gcc defaults macosx-version-min to be the system version. This, of course, can be substituted by taking the SDK version that matches the local system and specifying macosx-version-min.

​http://developer.apple.com/documentation/DeveloperTools/Conceptual/cross_development/HowItWorks/chapter_2_section_3.html

[René Rivera]

Most of this is already taken care of in the darwin.jam in trunk, and will be available for the 1.36.0 release. See changesets [46793] and [47066].