mpd: use upstream patches

This commit replaces 0002-musl-gcc5-fixes.patch by a backport of 3
upstream commits. It also renames
0001-thread-Name-include-stdio.h-for-prctl-as-well.patch to have the
sequence number 0004, so that it applies after the backported upstream
patches (since this patch is not upstream yet).

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>