Use target-os instead of os in Jamfiles

[Steve Soule <sts11dbxr@…>]

In many of the Jamfiles in Boost, the "os" property is used to add libraries and defines appropriate to the target operating system. But the "os" property doesn't give the target operating system; it gives the build operating system. The "target-os" property gives the target operating system. So these Jamfiles do the wrong thing when cross-compiling.

According to Vladimir Prus on the Boost-build mailing list:

"Yes, in most cases 'target-os' should be used. Please file bugs for libraries that use 'os'."

The full list of Boost libraries that appear to have this problem is:

asio iostreams thread

I generated this list by doing "grep 'import os'" and filtering out the python files, so it may not be all that accurate.

[anonymous]

Merge Building Boost with build tool.