Modify libc++/libc++abi/libunwind SONAMEs to include major version

In order to be able to install multiple major versions of libc++ and its dependencies libc++abi/libunwind at the same time (eg, libc++1-19 and libc++1-21), we need to have a unique library name for the libs. Simply changing the name of the library could potentially run into issues when packages that are built/tested on an older version of libc++ end up using a newer version when the admin installs newer libc++ major packages.

So instead, we modify the SONAME to include the major version so that when a package depends on, say, libc++1-19, its binaries actually run using /lib//libc++1.so.1.0.19 instead of whatever /lib//libc++1.so happens to point to.