distcc-avahi: --sbindir=/usr/bin for usr-merged Arch

Fixes install conflict with filesystem pkg on merged-usr systems where
/usr/sbin is a symlink to /usr/bin.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

arch/distcc-avahi/PKGBUILD

@@ -48,6 +48,7 @@ build() {
     export CXXFLAGS="${CXXFLAGS} -Wno-error"
     ./configure \
         --prefix=/usr \
+        --sbindir=/usr/bin \
         --sysconfdir=/etc \
         --mandir=/usr/share/man \
         --with-auth \