configure: GLIB_COMPILE_RESOURCES is wrong when cross-compiling.
AM_PATH_GLIB_2_0 m4 macro actually computes this value using
$PKG_CONFIG. Yet $PKG_CONFIG variable is the pkg-config tool looking for
target libraries (not host), hence it would return the executable
`glib-compile-resources` built for the target.
Also using the same variable name invalidates our test: our own
AC_PATH_PROG was never run as the variable was already set. And no
environment variable could override this test anymore either. This is
why I rename the test variable to HOST_GLIB_COMPILE_RESOURCES.
(cherry picked from commit
d1d9eb17e5c59f13f27ff1d906291d34b1022c9a)