Set LD_LIBRARY_PATH when running g-ir-compiler

Set LD_LIBRARY_PATH when running g-ir-compiler

g-ir-compiler currently opens the library for the .gir it is compiling;
to make that work we need to set LD_LIBRARY_PATH before running
g-ir-compiler to include .libs.

(I think this may have been working earlier because there was a
hack that substituted .so with .la and tried opening that; that
works for the incorrect libclutter-glx-1.0.so but not for the
correct libclutter-glx-1.0.so.0)

http://bugzilla.openedhand.com/show_bug.cgi?id=1771