Extend MYSQL_ADD_EXECUTABLE with new arguments, and use it for
generating *all* executables (including unit tests). Store all
executables in ${CMAKE_BINARY_DIR}/runtime_output_directory

New target copy_openssl_dlls, which copies OpenSSL DLLs to
runtime_output_directory. All tools/executables used during build
time depend on this (on windows only)

Rewrite the regex unit test to run all three tests by default, rather
than having three separate tests.

Fix unused/unmaintained plugin/keyring/keyring-test

Extend mtr to look for executables in
${CMAKE_BINARY_DIR}/runtime_output_directory.

The executable 'my_safe_process', used by mtr to start the server, is
the only executable *not* moved to runtime_output_directory.
This is in order to minimize the changes necessary to mtr.