libsframe: testsuite: add new tests for sframe_find_fre API

libsframe provides an API to find the FRE associated with a given PC in
the program.  This patch adds a direct test of this API.

In this test, we create two dummy SFrame FDEs with 4 FREs each.  Then we
test that sframe_find_fre () works for the first, second, third and the
last FRE from one of the FDEs.  Such a test ensures better regression
testing for the sframe_find_fre () function which is going to be the
bread and butter of an SFrame based stack tracer.

libsframe/
	* Makefile.in: Regenerated.
	* testsuite/libsframe.find/find.exp: New test.
	* testsuite/libsframe.find/findfre-1.c: New test.
	* testsuite/libsframe.find/local.mk: Build new test.
	* testsuite/local.mk: Include libsframe.find.