Makefile: pass PKG variable to build rules

See here for explanation:

http://www.gnu.org/software/make/manual/make.html#Target_002dspecific
package glib: build native tools only when not installed
package gnutls: automake 1.12 compatibility
package libglade: use configure and make options instead of patch and autoconf
update package gnutls
update package gcc
package poppler: use extra pkgconfig directory for qt
package poppler: use TARGET rather than assuming its value
package armadillo: fix update macro
update package armadillo
update package poppler
Merge pull request #83 from mabrand/stable-fix-gnutls

package gnutls: automake 1.12 compatibility
Merge branch 'stable'

Compatibility changes for Automake 1.12 of src/gnutls-1-fixes.patch from stable branch ignored.
Merge pull request #81 from tonytheodore/glib-optional-native

Review: Build glib native tools only if they're not installed
add s3-fetch-and-sync script
Merge branch 'master' of github.com:mxe/mxe
update package tiff
update package wt
Add Spek to the list of projects that use MXE
Merge pull request #85 from alexkay/master

Add Spek to the list of projects that use MXE