Pip Cet announced this weekend the work he's been doing on WebAssembly support within GCC, Glibc, and Binutils. Pip explained, "This binutils port produces and deals with ELF files containing WebAssembly code; WebAssembly modules (in the WebAssembly object file format) can be output using special linker scripts and -Obinary, but they cannot be used as input for any of the binutils programs at present. (While the gcc port, in particular, makes some decisions that negatively affect performance, the binutils port is quite general and should permit the assembly, linking, and manipulation of all WebAssembly code, provided it is still encapsulated in ELF files)."
More details on this WebAssembly work for the GNU toolchain via the Binutils mailing list. The code for this experimental work is hosted on GitHub.