It is safe to remove *-dev packages after building is done.
But only the *-dev packages, but removing the *-dev packages will also remove any packages automatically installed with the *-dev packages as dependencies.
libmcrypt-dev also installs
sudo apt-get -y install libmcrypt-dev # run your build commands here ... sudo apt-get -y purge libmcrypt-dev
will result in:
PHP Warning: PHP Startup: Unable to load dynamic library '/usr/local/lib/php/extensions/no-debug-non-zts-20151012/mcrypt.so' - libmcrypt.so.4: cannot open shared object file: No such file or directory in Unknown on line 0
So you need to ensure your library packages are installed separate:
sudo apt-get -y install libmcrypt-dev libmcrypt4 # run your build commands here ... sudo apt-get -y purge libmcrypt-dev