libsframe: testsuite: add tests for sframe_get_funcdesc_with_addr API

sframe_get_funcdesc_with_addr API is currently used internally by the
sframe_find_fre ().

In this test, we create three dummy SFrame FDEs with 4 FREs each.  Then,
we use few negative tests to lookup FREs with PCs not in the range of
PCs covered by the FDEs, ensuring graceful return from
sframe_get_funcdesc_with_addr in all cases.  Some positive tests are
also added that exercise further scenarios as well.

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