Assembly files: use .S extension, not .s (error "riscv64-unknown-elf-as: unrecognized option `-x')
When dealing with assembly files, you must use the extension .S (uppercase) since otherwise (using .s (lowercase)), you can have problems.
The error message is "riscv64-unknown-elf-as: unrecognized option `-x'" and then the final error: "... 'swervolf_nexys'" terminated with exit code: 1".
At first, I used .s extension with no problem, but nowaday this extension produces error. The solution is very easy: rename your file to .S
From the platformio error messages it is very difficult to deduce that the problem is the extension.