The present CMake logic wants to pass FIXED:NO to the linker for 64-bit
builds, which on the face of it seems like a Good Thing: it permits code to be
relocated in memory, preventing collisions if two libraries happen to want to
load into overlapping address ranges.

However the way it's being specified is wrong and harmful. Passing /FIXED:NO
to the compiler command line engages /FI (Forced Include!) of a nonexistent
file XED:NO -- producing lots of baffling fatal compile errors.

Thanks Callum for diagnosing this!

Evidently the LL_VIEWER_CHANNEL macro (defined on the compiler command line)
used to contain enclosing double quotes. Something changed (newer CMake
version?) so that the macro now expands as Second Life Release rather than as
"Second Life Release". That leads to syntax errors when it's used.

Add C++ preprocessor trickery to stringize the value of the macro.

Pull in new version of KDU third party package that is build (correctly) as a static library vs. a stub library/DLL

Specifically, DriverCallback() was accepting several DWORD arguments that
should really be DWORD_PTR arguments. In a 32-bit compile, evidently that was
okay, but for 64 bits they're different sizes.

We never intend to support 32-bit Mac builds any more.

This change eliminates the autobuild warning about not finding darwin64 and
therefore falling back on plain darwin.

Some day llmake() will be unnecessary because compiler deduction of class
template arguments from constructor arguments has been approved by ISO.

LLPrivateMemoryPool and LLPrivateMemoryPoolManager have assumed that it's
always valid to cast a pointer to U32. With 64-bit pointers, no longer true.

It's never been clear to me why Macs tend to refer to 32-bit Intel processors
as i386 when other platforms tend to refer to them as i686. New CMake logic to
derive ARCH from ADDRESS_SIZE produces i686. Give viewer_manifest.py a
Darwin_i686_Manifest class alias so it continues to work when arch is passed
as i686 as well as i386.

llcorehttp/tests had a clone of llmessage/tests/testrunner.py that was almost
identical save for recognizing an extra optional parameter. Migrate those few
lines into llmessage/tests/testrunner.py; eliminate the copy in llcorehttp;
help test_llcorehttp_peer.py find the testrunner.py in llmessage/tests.

which in turn depends on ADDRESS_SIZE.

There Must Be A Better Way.

With the new autobuild command infrastructure, the quotes that used to be
necessary for correct command-line parsing are now actually undesirable: they
are passed literally to the command in question, causing (e.g.) cmake to
complain that although it knows of a generator called Xcode, there's no
generator called 'Xcode'.

with tests on ADDRESS_SIZE, which is now set on the compiler command line.