Add dev notes

DEV.md

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+# M3/Wasm development notes
+
+
+## Build on Linux
+
+### Clang (recommended)
+
+```sh
+cmake -GNinja -DCLANG_SUFFIX="-9" ..
+ninja
+```
+
+### GCC
+
+```sh
+cmake -GNinja ..
+ninja
+```
+
+## Build on Windows
+
+You may need to install:
+- [Build Tools for Visual Studio 2019](https://visualstudio.microsoft.com/downloads/#build-tools-for-visual-studio-2019)
+- [Ninja](https://github.com/ninja-build/ninja/releases)
+- [Clang 9](https://releases.llvm.org/download.html#9.0.0)
+
+
+### Clang with Ninja (recommended)
+
+```bat
+cmake -GNinja -DCLANG_CL=1 ..
+ninja
+```
+
+### Clang with MSBuild
+
+```bat
+cmake -G"Visual Studio 16 2019" -A x64 -T ClangCL ..
+MSBuild /p:Configuration=Release wasm3.sln
+```
+
+### MSVC with MSBuild
+
+```bat
+cmake -G"Visual Studio 16 2019" -A x64 ..
+MSBuild /p:Configuration=Release wasm3.sln
+```
+
+### MSVC with Ninja
+
+```bat
+cmake -GNinja ..
+ninja
+```