Support Alpine Linux as a platform

Alpine Linux is a security-oriented, lightweight Linux distribution based on musl libc and busybox.

Alpine Linux is a very popular Linux distribution in the container universe of Docker.
There are many requests to port the current MariaDB image to Alpine Linux. This have already been done for the PostgeSQL image, where the size for the Alpine variant is about 20MB and 120MB for the Debian variant.

Alpine Linux currently requires some patches to build MariaDB.
Please consider merging this patches upstream and adding officially support for the Alpine platform. Or even better, provide prebuilt packages.