Making it obvious which of the two operations is performed, reducing
call args and making sure a global isn't defined multiple times via
`defineGlobal()`.
The only [intended] functional change is in gen/trycatchfinally.cpp,
where I inserted a check for an existing __cpp_type_info_ptr global when
emitting a catch for C++ exceptions.
See https://llvm.org/bugs/show_bug.cgi?id=25162
However LLVM inliner now knows not to inline functions inside cleanup pads and so this is no longer needed. I have tested with clang (trunk) and clang also no longer marks function calls explicitly with noinline: the inliner no longer tries to inline `alwaysinline` functions.
The change is necesary because setting `noinline` conflicts with functions that have `alwaysinline` attribute added (due to `pragma(inline, true)`).
- do not inline functions into the cleanup funclets, it can break exception handling
- even if no var given, retrieve the caught exception to pass it to _d_eh_enter_catch
