shairport-sync: add upstream patch to fix soxr configure issue

shairport-sync: add upstream patch to fix soxr configure issue

Commit e047dee241fe0660d92311a124757065c6c4c93d adds an upstream patch
to fix a build issue with soxr.  The patch also adds detecting soxr
using pkg-config. Upstream detected an config issue [1], where the
resulting binary lacks soxr support, although libsoxr was correctly
detected.

This patch adds a define for `HAVE_LIBSOXR` when using pkg-config.

Backported from: cd6a99a7cfde1c5e1c1cc74ee6a77041bb4012d9

[1] https://github.com/mikebrady/shairport-sync/issues/740

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>