qt4-b-gone: Remove bundled sha512 implementation Qt5 supports SHA512 natively, so we no longer need to ship an external implementation.
Add support for SHA2-512 hash on Qt4 builds Qt4 doesn't support anything higher than SHA1 in QCryptographicHash, so it is necessary to include a fallback. This bundles sha512.c from PolarSSL/mbed TLS. It is only used for Qt4 builds and does not require a dependency on external libraries that might be hard to compile on Windows® or Mac OSX®. It can be removed once Qt4 is no longer supported.