https://reviews.llvm.org/rG5369517d20dd362a178a1b2d6c398d8898ee4620
bumped the version number in __config to 13000, causing a test failure
in libcxx/test/libcxx/libcpp_version.pass.cpp because now the two
don't match.
This is the only part of the post-release TODO in
libcxx/docs/Contributing.rst that wasn't done by that commit.
This patch does two seperate things. First it adds a file called
"__libcpp_version" which only contains the current libc++ version
(currently 4000). This file is not intended for use as a header. This file
is used by Clang in order to easily determine the installed libc++ version.
This allows Clang to enable/disable certain language features only when the
library supports them.
The second change is the addition of _LIBCPP_LIBRARY_VERSION macro, which
returns the version of the installed dylib since it may be different than
the headers.
llvm-svn: 285382
Simon Tatham