gas: sframe: fix PR gas/33170

gas: sframe: fix PR gas/33170

SFrame generation code assumes that since DW_CFA_restore means
restoration of the state of the register to the one at the beginning of
the function, there must be a state to restore to (hence the gas_assert
(cie_fre)).

This assumption needs adjustment.  DW_CFA_restore may be present in the
very beginning of a (e.g., cold) function, with no initialized state for
SFrame functions to restore to.

gas/
	PR gas/33170
	* gas/gen-sframe.c (sframe_xlate_do_restore): Use current FRE if
	CIE FRE is not yet setup.
gas/testsuite/
	PR gas/33170
	* gas/cfi-sframe/cfi-sframe.exp: New test.
	* gas/cfi-sframe/cfi-sframe-x86_64-pr33170.d: New test.
	* gas/cfi-sframe/cfi-sframe-x86_64-pr33170.s: New test.