Wasmer OS distro packaging notes

Wasmer is written in Rust. To build Wasmer, where possible, do not directly invoke cargo, but use the supplied Makefile
Wasmer provides several compilers and the Makefile autodetects when compilers can be compiled and/or installed. Set the environment variables ENABLE_{CRANELIFT,LLVM,SINGLEPASS}=1 to force compiler to be build or to fail trying, e.g:
sh
```
$ ENABLE_LLVM=1 make build-wasmer
```
make install respects DESTDIR, but prefix must be configured with WASMER_INSTALL_PREFIX. Note that DESTDIR must include WASMER_INSTALL_PREFIX, e.g.:
sh
```
export WASMER_INSTALL_PREFIX=/usr
make
DESTDIR=/tmp/staging/usr make install
```
In case you must build/install directly with cargo, make sure to enable at least one compiler feature, like e.g. --features cranelift,
- Beware that compiling with cargo build --workspace --features … will not enable features on the subcrates in the workspace and result in a headless Wasmer binary that can not compile Wasm files directly.
For reproducible builds, set WASMER_REPRODUCIBLE_BUILD=1 in the build environment. This strips the build timestamp from wasmer --version -v by omitting the verbose commit-date: line, which is useful for distribution packaging.
If you split the package into several subpackages, beware that the create-exe command of the wasmer CLI requires libwasmer.a to be installed at $WASMER_INSTALL_PREFIX/lib/libwasmer.a. Suggestions for splitting:
- The wasmer-headless CLI contains a subset of the wasmer's functionalities and should only be packaged when splitting — it must be built explicitly with:
  sh
```
$ make build-wasmer-headless-minimal install-wasmer-headless-minimal
```
- libwasmer, containing libwasmer.so*,
- libwasmer-dev, containing the header files and a .pc file,
- libwasmer-static, containing libwasmer.a.

The Wasmer distro packaging story is still in its infancy, so feedback is very welcome.

Miscellaneous: binfmt_misc

Wasmer can be registered as a binfmt interpreter for wasm binaries. An example systemd .service is included here. Please consider statically linking the wasmer binary so that this capability is also available in mount namespaces.