[CFLAA] Add interprocedural function summaries.

This patch adds function summaries, so that we don't need to recompute
various properties about function parameters/return values at each
callsite of a function. It also adds many interprocedural tests for
CFLAA.

Patch by Jia Chen.

Differential Revision: http://reviews.llvm.org/D21475#inline-182390