xfce4-sensors-plugin builds a broken pkgconfig file using
./configure --prefix=/usr \
	--sysconfdir=/etc \
	--libexecdir=/usr/lib \
	--localstatedir=/var \
	--disable-static \
	--with-pathhddtemp=/usr/sbin/hddtemp \
	--disable-debug

/usr/lib/pkgconfig/libxfce4sensors-1.0.pc has
prefix=/usr
exec_prefix=${prefix}
datadir=${datarootdir}
libdir=${exec_prefix}/lib
includedir=${prefix}/include
libexecdir=/usr/lib
localedir=${datarootdir}/locale
datarootdir=${prefix}/share

Because @datadir@ refers to no yet set @datarootdir@ the .pc file breaks some other interaction. See https://bugs.archlinux.org/task/24911 for downstream report.