Add extra field to gtm_jmpbuf on x86 only

Add extra field to gtm_jmpbuf on x86 only

Expand the gtm_jmpbuf structure by one word field to add
Intel CET support further. The code in sjlj.S already
allocates more space on the stack then gtm_jmpbuf needs.
Use this extra space to absorb the new field.

The structure is allocated on the stack in such a way
that eip/rsp field is overlapped with return address on
the stack. Locate the new field right before eip/rsp so
code that accesses buffer fields relative to address of
gtm_jmpbuf has its offsets unchanged.

	* libitm/config/x86/target.h: Add new field (ssp).
	* libitm/config/x86/sjlj.S: Change offsets.

From-SVN: r254907