Initial implementation of msvc-go-wine

A single-binary Go tool for cross compiling with the real MSVC toolchain
on Linux via Wine. Behaves as cl/link/lib/rc/midl/mt/dumpbin/msbuild/
nmake/ml/ml64/armasm/armasm64/cmd/findstr depending on the name it's
invoked as, plus download/install/env/version management subcommands.

- download: fetches the MSVC/WinSDK installer manifest, resolves package
  selection and dependencies, downloads and verifies payloads, unpacks
  VSIX/MSI packages, and applies a handful of compatibility patches so
  VsDevCmd.bat and MSBuild's SDK detection work without a Windows
  Registry (which doesn't exist under Wine).
- install: locates the installed toolchain/SDK versions, normalizes
  header/library name casing, lays out per-architecture tool symlinks
  with an env.json config each, and compiles a small native launcher
  (toolrelay.exe) that lets mt.exe's CMake-compatibility exit code
  survive Wine's own exit-code truncation.
- The wrapper runtime rewrites absolute unix paths in tool arguments into
  Wine's z:\... form, runs the real .exe under wine, and rewrites the
  tool's output back to plain unix paths.

Verified end-to-end against a real MSVC/WinSDK download: cl, link, mt and
the resulting hello.exe all work under Wine, including through the
toolrelay.exe relay path and with paths containing non-ASCII characters.

Offline unit tests cover the wrapper's path-rewrite/output-filter logic,
install-time header lowercasing, and download package-selection/
dependency-resolution.

internal/wrapper/tools.go

@@ -0,0 +1,58 @@
+// Package wrapper implements the per-tool command dispatch (cl, link, lib,
+// ml, ml64, mc, midl, mt, rc, dumpbin, msbuild, nmake, armasm, armasm64, cmd,
+// findstr): loading each tool's environment, invoking it under Wine, and
+// filtering its output.
+package wrapper
+
+import "github.com/Cheviiot/msvc-go-wine/internal/wineenv"
+
+// dirKind selects which install directory a tool's real .exe lives in.
+type dirKind int
+
+const (
+	dirBin dirKind = iota // <bindir> - vc/tools/msvc/<ver>/bin/Host<host>/<arch>
+	dirSDK                // <sdkbindir> - kits/10/bin/<sdkver>/<host>
+	dirMSBuild
+)
+
+type spec struct {
+	exeName      string
+	dir          dirKind
+	rawStdout    bool // MSBuild: skip line filtering, inherit stdio directly
+	stdoutFilter lineFilter
+	stderrFilter lineFilter
+	postProcess  func(origArgs []string) // cl: fix up /P /Fi<file> output
+}
+
+// Tools lists every multi-call name this binary answers to, besides its own
+// management-CLI name.
+var Tools = map[string]spec{
+	"cl":       {exeName: "cl.exe", dir: dirBin, stdoutFilter: clStdoutFilter, stderrFilter: clStderrFilter, postProcess: clPostProcess},
+	"link":     {exeName: "link.exe", dir: dirBin},
+	"lib":      {exeName: "lib.exe", dir: dirBin},
+	"ml":       {exeName: "ml.exe", dir: dirBin},
+	"ml64":     {exeName: "ml64.exe", dir: dirBin},
+	"nmake":    {exeName: "nmake.exe", dir: dirBin},
+	"armasm":   {exeName: "armasm.exe", dir: dirBin},
+	"armasm64": {exeName: "armasm64.exe", dir: dirBin},
+	"dumpbin":  {exeName: "dumpbin.exe", dir: dirBin, stdoutFilter: dumpbinStdoutFilter},
+	"mc":       {exeName: "mc.exe", dir: dirSDK},
+	"midl":     {exeName: "midl.exe", dir: dirSDK},
+	"mt":       {exeName: "mt.exe", dir: dirSDK},
+	"rc":       {exeName: "rc.exe", dir: dirSDK},
+	"msbuild":  {exeName: "MSBuild.exe", dir: dirMSBuild, rawStdout: true},
+}
+
+// nativeTools are handled entirely without Wine.
+var nativeTools = map[string]bool{"cmd": true, "findstr": true}
+
+func (s spec) exeDir(p *wineenv.Paths) string {
+	switch s.dir {
+	case dirSDK:
+		return p.SDKBinDir
+	case dirMSBuild:
+		return p.MSBuildBinDir
+	default:
+		return p.BinDir
+	}
+}