NEWS: sframe: mention new semantics for SFrame FDE function start addr

NEWS: sframe: mention new semantics for SFrame FDE function start addr

The SFrame FDE's function start address is always emitted as follows by
GAS and ld:  it is the offset of the start PC of the respective function
from the FDE field itself.

GAS and ld will emit a flag SFRAME_F_FDE_FUNC_START_PCREL set to 1
when emitting the field in this encoding.

	* binutils/NEWS: Announce the change of encoding for SFrame FDE
	  func start addr field.
        * gas/NEWS: Announce the emission of new flag
	  SFRAME_F_FDE_FUNC_START_PCREL.
        * ld/NEWS: Likewise.  Relocatable links are now fixed.