Parts of this were discussed in the context of Andrew's CET-SS work.
Further parts simply fit the underlying picture. And the two final
patches get attached here simply because of their dependency: Patch
4 was sent standalone already as v2, and is unchanged from that,
while patch 6 is new.
1: replace __ASM_{CL,ST}AC
2: reduce CET-SS related #ifdef-ary
3: drop ASM_{CL,ST}AC
4: fold indirect_thunk_asm.h into asm-defns.h
5: guard against straight-line speculation past RET
6: limit amount of INT3 in IND_THUNK_*
Jan
