[BOLT rebase] Rebase fixes on top of LLVM Feb2018

Summary:
This commit includes all code necessary to make BOLT working again
after the rebase. This includes a redesign of the EHFrame work,
cherry-pick of the 3dnow disassembly work, compilation error fixes,
and port of the debug_info work. The macroop fusion feature is not
ported yet.

The rebased version has minor changes to the "executed instructions"
dynostats counter because REP prefixes are considered a part of the
instruction it applies to. Also, some X86 instructions had the "mayLoad"
tablegen property removed, which BOLT  uses to identify and account
for loads, thus reducing the total number of loads reported by
dynostats. This was observed in X86::MOVDQUmr. TRAP instructions are
not terminators anymore, changing our CFG. This commit adds compensation
to preserve this old behavior and minimize tests changes. debug_info
sections are now slightly larger. The discriminator field in the line
table is slightly different due to a change upstream. New profiles
generated with the other bolt are incompatible with this version
because of different hash values calculated for functions, so they will
be considered 100% stale. This commit changes the corresponding test
to XFAIL so it can be updated. The hash function changes because it
relies on raw opcode values, which change according to the opcodes
described in the X86 tablegen files. When processing HHVM, bolt was
observed to be using about 800MB more memory in the rebased version
and being about 5% slower.

(cherry picked from FBD7078072)