This patch adds a new pseudo-op - .seh_code - to structured exception handling

This patch adds a new pseudo-op - .seh_code - to structured exception handling
suite of ops.  It changes the current section back to the code section of the
current function.  This is helpful because the code section may not be .text.

	* config/obj-coff-seh.c (obj_coff_seh_code): New function -
	switches the current segment back to the code segment recorded
	when seh_proc was last invoked.
	* config/obj-coff-seh.h (SEH_CMDS): Add seh_code.