Add buildscript

[jgonet]

Instead of building using command line and cmake/make/emcmake/emmake, streamline to use single script.

➜  AtomVM git:(swm) ✗ ./build-fission.sh
Usage: ./build-fission.sh [--clean] <build_mode>
Options:
  --clean       - Clean project before building
Build modes:
  debug-unix    - Debug build for Unix platforms
  debug-wasm    - Debug build for WebAssembly
  release-unix  - Release build for Unix platforms
  release-wasm  - Release build for WebAssembly

These changes are made under both the "Apache 2.0" and the "GNU Lesser General
Public License 2.1 or later" license terms (dual license).

SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later

[mat-hek]

I get the following error trying to run the script: ninja: error: loading 'build.ninja': No such file or directory

[bblaszkow06]

I get the following error trying to run the script: ninja: error: loading 'build.ninja': No such file or directory

You must delete build and src/platforms/emscripten/build to regenerate cmake with new env var and generate build.ninja

BTW I would suggest

1. Separating directories for each output type to know which version is currently in out
2. Use separate build dirs to not regenerate cmake from scratch when changing the build. If both of them would be different then build, it could be left out for manual compilation (e.g. when experimenting with cmake flags) and would prevent the error that @mat-hek saw

[mat-hek]

BTW the script could support passing CMake flags