This avoids doing a Triple -> std::string -> Triple round trip in lots
of places, now that the Module stores a Triple.

The module currently stores the target triple as a string. This means
that any code that wants to actually use the triple first has to
instantiate a Triple, which is somewhat expensive. The change in #121652
caused a moderate compile-time regression due to this. While it would be
easy enough to work around, I think that architecturally, it makes more
sense to store the parsed Triple in the module, so that it can always be
directly queried.

For this change, I've opted not to add any magic conversions between
std::string and Triple for backwards-compatibilty purses, and instead
write out needed Triple()s or str()s explicitly. This is because I think
a decent number of them should be changed to work on Triple as well, to
avoid unnecessary conversions back and forth.

The only interesting part in this patch is that the default triple is
Triple("") instead of Triple() to preserve existing behavior. The former
defaults to using the ELF object format instead of unknown object
format. We should fix that as well.

Identified with misc-include-cleaner.

Previously this took a reference to a map and returned a bool to say
whether it succeeded. We can return a StringMap instead, as all callers
but 1 simply iterated the map if the bool was true, and passed in empty
maps as the starting point.

lldb's lit-cpuid did specifically check whether the call failed, but due
to the way the x86 routines work this works out the same as checking if
the returned map is empty.

Replace it with a forward declaration instead. Analysis.h is pulled in
by all passes, but not all passes need to access the module.

This will make it easy for callers to see issues with and fix up calls
to createTargetMachine after a future change to the params of
TargetMachine.

This matches other nearby enums.

For downstream users, this should be a fairly straightforward
replacement,
e.g. s/CodeGenOpt::Aggressive/CodeGenOptLevel::Aggressive
or s/CGFT_/CodeGenFileType::

Currently clangDriver passes -femulated-tls and -fno-emulated-tls to cc1.
cc1 forwards the option to LLVMCodeGen and ExplicitEmulatedTLS is used
to decide the value. Simplify this by moving the Clang decision to
clangDriver and moving the LLVM decision to InitTargetOptionsFromCodeGenFlags.

The forwarding header is left in place because of its use in
`polly/lib/External/isl/interface/extract_interface.cc`, but I have
added a GCC warning about the fact it is deprecated, because it is used
in `isl` from where it is included by Polly.

Even with D129349 <https://reviews.llvm.org/D129349>, various SPARC JIT
tests still `FAIL`.  They are guarded by `host-supports-jit`.  This is set
from `clang-repl --host-supports-jit` which still returns `true`.  It turns
out the `JITTargetMachineBuilder` doesn't consider `hasJIT` at all.

This patch corrects this, turning the affected tests `UNSUPPORTED`.

Tested on `sparcv9-sun-solaris2.11`.

Differential Revision: https://reviews.llvm.org/D129350