libglib2: don't build tests

Add a patch that provides an additional --disable-tests option to the
configure script.

Disabling the build of tests has two benefits:
 * Prevents the build of a lot of code that doesn't build on noMMU
   platforms.
 * Reduces the build time.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>