I just noticed that the mixxx 9999 ebuild is broken in the overlay.
The fix is very simple, just delete the cflags patch.
diff --git a/var/lib/layman/pro-audio/media-sound/mixxx/mixxx-9999.ebuild b/./mixxx-9999.ebuild
index dd18816..b99b00b 100644
--- a/var/lib/layman/pro-audio/media-sound/mixxx/mixxx-9999.ebuild
+++ b/./mixxx-9999.ebuild
@@ -56,7 +57,6 @@ DEPEND="${RDEPEND}
S=${S}/${PN}
src_prepare() {
- epatch "${FILESDIR}"/${P}-cflags.patch
epatch "${FILESDIR}"/${P}-system-libs.patch
epatch "${FILESDIR}"/${P}-docs..patch