gas: sframe: handle .cfi_undefined

Fix PR gas/32952 - sframe: incorrect handling of .cfi_undefined in gas

In context of SFrame generation, it is incorrect to simply ignore all
.cfi_undefined.  We may ignore only those .cfi_undefined which are for
registers of no interest (similar to whats done for other CFI
directives).

gas/
        * gen-sframe.c (sframe_xlate_do_cfi_undefined): New definition.
        (sframe_do_cfi_insn): Handle .cfi_undefined.
gas/testsuite/
        * gas/cfi-sframe/cfi-sframe.exp: Add new tests.
        * gas/cfi-sframe/cfi-sframe-common-10.d: New test.
        * gas/cfi-sframe/cfi-sframe-common-10.s: New test.
	* gas/cfi-sframe/cfi-sframe-x86_64-empty-4.d: New test.
	* gas/cfi-sframe/cfi-sframe-x86_64-empty-4.s: New test.