X86: permit using SjLj EH on x86 targets as an option

This adds support to the backed to actually support SjLj EH as an exception
model.  This is *NOT* the default model, and requires explicitly opting into it
from the frontend.  GCC supports this model and for MinGW can still be enabled
via the `--using-sjlj-exceptions` options.

Addresses PR27749!

llvm-svn: 271244
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 7a59645..9e97d7b 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2388,6 +2388,7 @@
 static bool isCatchAll(EHPersonality Personality, Constant *TypeInfo) {
   switch (Personality) {
   case EHPersonality::GNU_C:
+  case EHPersonality::GNU_C_SjLj:
   case EHPersonality::Rust:
     // The GCC C EH and Rust personality only exists to support cleanups, so
     // it's not clear what the semantics of catch clauses are.
@@ -2399,6 +2400,7 @@
     // match foreign exceptions (or didn't, before gcc-4.7).
     return false;
   case EHPersonality::GNU_CXX:
+  case EHPersonality::GNU_CXX_SjLj:
   case EHPersonality::GNU_ObjC:
   case EHPersonality::MSVC_X86SEH:
   case EHPersonality::MSVC_Win64SEH: