Use -sv or recognise SystemVerilog files

[concavegit]

I am using a source with an always_comb block which only builds when I change it to always @* and rename the file from foo.sv to foo.v.
Looking through the builder, it looks like only .v extensions are recognixed, rather than .sv which would enable systemverilog files.
A solution to build systemverilog files is to recognize .sv as a source suffix, or find some other way to pass -sv to yosys.