Fix MSVC build

Added _WIN32 guards to new platform features. Using correct SetErrorStringWithFormat within Host when LLDB_DISABLE_POSIX is defined. Also fixed an if defined block.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@195766 91177308-0d34-0410-b5e6-96231b3b80d8
Update gitignore to be effective.
Factorize build settings in external xcconfig files.
Doing this greatly reduces the number of duplicated settings, as 'SDK' specific settings can be specified only once instead of once per Build Configuration.

This also fix a couple of issues with 10.9 SDK and python (which was already fixed for some targets but not all).
fixup (to support llvm symlink)
Sync project.
Add debugger packages support.
Useful args from debugserver

Summary:

Reviewers:

CC: