Toolchain bump and rebuild of all packages, switch to MariaDB and libjpeg-turbo

To mitigate the known vulnerabilities Spectre v1-v3 we bumped gcc to version 7.3 and enabled some hardening compile flags als also bumped the whole toolchain glibc to version 2.27, binutils to version 2.30 and all major languages. Ffmpeg bumped to 3.4.x and the Linux kernel to version 4.15.4. That lead to a mass rebuild of all packages. While at it we did the long overdue switch from MySQL do MariaDB and from libjpeg to libjpeg-turbo. Please be patient while the merge is running, as you might break everything if you update in the middle.