libsframe: testsuite: add sframe_find_fre tests for pltN entries

Add a new test plt-findfre-1 to ensure lookup of SFrame stack trace
information for pltN entries is correct.

In this test, a dummy SFrame FDE of type SFRAME_FDE_TYPE_PCMASK is
created.  The size of the 'function code block' covered by the SFrame
FDE is equivalent to 5 pltN entries of 16 bytes each.

The test first looks up SFrame FREs for some addresses in the first pltN
entry, followed by lookups for some addresses in the fourth pltN entry.

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