Adds three new cross-platform instruction creation macros, XINST_CREATE_add_sll(), XINST_CREATE_jump_cond() and XINST_CREATE_slr_s(), for use in drcachesim.
For XINST_CREATE_jump_cond(), we add aliases so that the same DR_PRED_* constants can be used for x86 as are used on aarchxx.
Adds x86 tests. The infrastructure for easily adding ARM (#1686 (closed)) and AArch64 (#2443) tests is still missing, unfortunately.