Could we avoid hardcoding brewisms on macOS?

[barracuda156]

CMakeLists now hardcodes Homebrew-specific paths:

if (${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
  add_compile_definitions(_XOPEN_SOURCE_EXTENDED)
  list(APPEND CMAKE_PREFIX_PATH /usr/local/opt/ncurses)
  list(APPEND CMAKE_PREFIX_PATH /opt/homebrew/opt/ncurses)
  list(APPEND OPENSSL_ROOT_DIR /usr/local/opt/openssl)
  list(APPEND OPENSSL_ROOT_DIR /opt/homebrew/opt/openssl)

It is undesirable to hardcode any paths, alien to the OS itself, unconditionally. Consider that someone has installed both Homebrew and another package manager (MacPorts, pkgsrc or you name it), and installs nmail from the latter. This gonna end up in opportunistic linking to brew libraries.