Fix ICU compile test for MinGW by adding the INCLUDE and LIB environment
variables to the compiler flags. The logic is the same as in qmodule.pri.

Task-number: QTBUG-34971
Change-Id: I192e06643517087587ec4a5dffe4698c2078011a
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>