Fix FastDebug builds linking the non-redistributable debug CRT (#7919)

* fix FastDebug QtFRED linking the debug CRT

FastDebug builds in the DLL-runtime tree (used whenever qtFRED is
enabled) compiled with /MDd and, since #7450, linked Qt's debug
libraries.  Both import ucrtbased.dll, MSVCP140D.dll and
VCRUNTIME140D.dll, which Microsoft does not license for redistribution,
so end users could not run the FastDebug qtFRED shipped in nightlies
and releases.  Static Qt is ruled out by the LGPL, so the only shippable
shape is the release CRT plus release Qt.

On MSVC, _DEBUG is the CRT's own contract: /MTd and /MDd define it
themselves, and the STL headers select msvcprtd.lib and
_ITERATOR_DEBUG_LEVEL=2 from it.  Stop force-defining it for FastDebug
on MSVC; the engine keys its debug behaviour on NDEBUG, and the few
_DEBUG guards in code/ are switched to NDEBUG so they keep working.
The static tree is unchanged: /MTd still defines _DEBUG there.

Fixes #7915

Co-Authored-By: Claude Fable 5.1 <[email protected]>

* derive the MSVC runtime choice once

The "DLL runtime or not" condition was spelled out in the toolchain and
twice in fred2 with "keep in sync" comments, and gtest_force_shared_crt
and antlr4's WITH_STATIC_CRT had already drifted: they only looked at
MSVC_USE_RUNTIME_DLL, so a qtFRED tree with tests enabled would have
asked both for the static CRT.  That is harmless today only because our
flag strings carry no literal /MD for them to rewrite.

Compute FSO_MSVC_RUNTIME_DLL once in toolchain-msvc.cmake and use it
everywhere.  InstallRequiredSystemLibraries deliberately stays keyed on
MSVC_USE_RUNTIME_DLL: the qtFRED deploy ships no compiler runtime.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

* remove FastDebug runtime leftovers

The /MD -> /MDd substitution on the FastDebug flag strings has done
nothing since the runtime moved to CMAKE_MSVC_RUNTIME_LIBRARY: the
Release flags it copies contain no runtime switch.  The commented-out
_ITERATOR_DEBUG_LEVEL=0 lines for gtest and the OpenXR loader belong to
the scheme #7450 removed from the toolchain.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

* use the release CRT for all FastDebug builds

Microsoft's documentation marks the static debug libraries (libcmtd,
libucrtd, libvcruntimed) "Not redistributable" and states that debug
versions of an application may only be copied to machines used for
testing, and the license grants distribution rights only for code on
the REDIST list, which contains no debug library in any form.  So the
statically linked FastDebug game and FRED2 are no more shippable than
the /MDd qtFRED was.

Link every FastDebug build against the release runtime.  The engine's
debug behaviour keys on NDEBUG, which FastDebug still leaves undefined,
so asserts, warnings and mprintf are unaffected; only the debug CRT's
heap checking goes, and that remains available in Debug builds.  FRED2's
static MFC library follows the CRT: the debug variant requires the debug
runtime.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

* keep the debug icon, version flag and FRED2 asserts without _DEBUG

The resource compiler only ever sees the explicit definitions, so with
_DEBUG no longer defined for FastDebug the game lost its debug icon and
both editors lost the VS_FF_DEBUG version flag.  Key those on NDEBUG,
which FastDebug still leaves undefined.

FRED2 also used MFC's ASSERT, VERIFY, ASSERT_VALID and TRACE0, which are
all compiled out without _DEBUG.  Convert them to the FSO equivalents
FRED2 already uses nearly everywhere else: Assert, Verify, a null check
in place of ASSERT_VALID (AssertValid only exists in debug MFC), and
mprintf.  The AssertValid/Dump overrides and DEBUG_NEW stay under
_DEBUG, as they must.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

---------

Co-authored-by: Claude Fable 5.1 <[email protected]>

code/exceptionhandler/exceptionhandler.cpp

@@ -381,7 +381,7 @@ int __cdecl RecordExceptionInfo(PEXCEPTION_POINTERS data, const char *Message)
 
 		wsprintf(DebugMessage, "%s location %08x caused an access violation.\r\n", readwrite, Exception->ExceptionInformation[1]);
 
-#ifdef	_DEBUG
+#ifndef NDEBUG
 		// The VisualC++ debugger doesn't actually tell you whether a read
 		// or a write caused the access violation, nor does it tell what
 		// address was being read or written. So I fixed that.

code/graphics/2d.cpp

@@ -2278,7 +2278,7 @@ bool gr_init(std::unique_ptr<os::GraphicsOperations>&& graphicsOps, GraphicsAPI
 // built in debug mode.  This helps if you run with the debugger active as the
 // game won't be switching from fullscreen to minimized every time you hit a breakpoint or
 // warning message.
-#ifdef _DEBUG
+#ifndef NDEBUG
 #ifdef _FORCE_DEBUG_WIDESCREEN
 	width = 1280;
 	height = 800;

code/model/modelread.cpp

@@ -3456,7 +3456,7 @@ int model_load(const  char* filename, ship_info* sip, ErrorType error_type, bool
 
 	pm->used_this_mission++;
 
-#ifdef _DEBUG
+#ifndef NDEBUG
 	if(Fred_running && Parse_normal_problem_count > 0)
 	{
 		char buffer[100];