Make LDC work with LLVM trunk (s/LinkOnceLinkage/LinkOnceOdrLinkage/) Also moved the #defines for linkage types into a separate header instead of mars.h so we can #include revisions.h without having to rebuild the entire frontend every time we update. (I'm using revisions.h to get the LLVM revision for use in preprocessor conditionals. It should work with LLVM release 2.5, old trunk and new trunk)

use rebuild with -dc=ldc-posix to build the demos