configure: prevent premature HAVE_GLU check
configure: prevent premature HAVE_GLU check

When cairo-gl and mesa-glu are present on the system, autoconf successfully
recognizes both. However, I was wondering why weston-screensaver was not
building since autoconf reported all dependencies were met.

Move the mesa-glu PKG_CHECK before the conditional. Additionally, remove
redundant check for enable_egl, as it is implied when GLU is 'yes.'

Signed-off-by: Joe Konno <a81ddd8a3c0bd1583a333acdc9e7599f7063b6e9@intel.com>

jonnylamb/weston,mchalupa/weston,kwm81/weston,Gnurou/weston,eyolfson/weston,krezovic/weston,giucam/weston,sir-murray/weston,udoprog/weston,Gnurou/weston,udoprog/weston,xorgy/weston,kwm81/weston,Tarnyko/weston-xdg_surface_present,mchalupa/weston,Fantu/compositor-spice,xorgy/weston,sir-murray/weston,giucam/weston,eyolfson/weston,Fantu/compositor-spice,jonnylamb/weston,krezovic/weston,Tarnyko/weston-xdg_surface_present,Fantu/compositor-spice