RFR: JDK-8058631 Rename posix to unix in build system to match file name changes

Wed Sep 24 12:39:10 UTC 2014

After Jigsaw M1, there is a new common "unix" directory structure. We 
have used "posix" in the build system for the same purpose, but this 
leads to unnecessary conversations. Instead, we should use "unix" all 
way through in the build system.

Also, this means that OS_API is slightly misleading -- we're not 
actually checking for an API such as POSIX, but the general category of 
OSes. I'll rename the *_OS_API to *_OS_TYPE instead. The "winapi" OS_API 
was never used, and is removed -- we only need to check for "windows", 
there's no need to introduce an abstract "winapi" category.

Bug: https://bugs.openjdk.java.net/browse/JDK-8058631
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8058631-rename-posix-to-unix/webrev.01

/Magnus