Build native Windows packages for both RDNA4 targets

Add explicit gfx1200/gfx1201 builds, runtime selection and per-target
code objects. Guard staging, packaging and installation against mixed
architectures; retain gfx1201 compatibility and strict K/M arithmetic.

Adapt realdody's target configuration and MSVC binary16/BOOL portability
fixes from ae530b0. Do not import its forced gfx12 layout on RDNA3.
Add exhaustive binary16 and C++/PowerShell target contract regressions.

Validation: 20 CTest gates on RX 9070 XT; four software-only gfx1200 gates;
MSVC portability compile checks; exact 4K K async and M control outputs;
isolated package install/restore and mixed-target rejection tests.
No physical gfx1200 validation is claimed.

Co-authored-by: realdody <[email protected]>

scripts/windows/gpu-target.ps1

@@ -0,0 +1,26 @@
+# Shared by the build, diagnostics, staging and game package scripts.
+function Get-D4RGpuTarget([string]$Root, [string]$Requested) {
+    $configured=$null
+    $targetFile=Join-Path $Root 'gpu-target.json'
+    if (Test-Path -LiteralPath $targetFile) {
+        $configured=(Get-Content -LiteralPath $targetFile -Raw | ConvertFrom-Json).architecture
+        if ($configured -notin @('gfx1200','gfx1201')) { throw "Unsupported package GPU target: $configured" }
+    }
+    $target=if ($Requested) { $Requested } elseif ($configured) { $configured } else { 'gfx1201' }
+    if ($target -notin @('gfx1200','gfx1201')) { throw "Unsupported GPU target: $target" }
+    if (!$configured -and $target -ne 'gfx1201') { throw 'A gfx1200 build requires gpu-target.json; rebuild with -GpuArch gfx1200.' }
+    if ($configured -and $target -ne $configured) { throw "Requested $target differs from package target $configured" }
+    return $target
+}
+function Assert-D4RCodeObjectTarget([string]$Path, [string]$Target) {
+    if ($Target -notin @('gfx1200','gfx1201')) { throw "Unsupported GPU target: $Target" }
+    $reader=[IO.BinaryReader]::new([IO.File]::OpenRead($Path))
+    try { $header=$reader.ReadBytes(64) } finally { $reader.Dispose() }
+    if ($header.Length -ne 64 -or $header[0] -ne 127 -or $header[1] -ne 69 -or $header[2] -ne 76 -or $header[3] -ne 70 -or
+        $header[4] -ne 2 -or $header[5] -ne 1 -or $header[18] -ne 224 -or $header[19] -ne 0) {
+        throw "Invalid AMDGPU ELF64 code object: $Path"
+    }
+    # LLVM AMDGPU e_flags machine IDs; inspect, never patch or spoof them.
+    $expected=if ($Target -eq 'gfx1200') { 0x48 } else { 0x4e }
+    if ($header[48] -ne $expected) { throw "Code object does not target ${Target}: $Path (ELF machine=$($header[48]))" }
+}