meson: Test for RISC-V assembler support

Support for '.option arch' directive [0] was added to binutils in d3ffd7f77654adafe5f1989bdfdbe4a337ff2e8b [1] and in llvm in 9e8ed3403c191ab9c4903e8eeb8f732ff8a43cb4 [2].

[0] https://github.com/riscv-non-isa/riscv-asm-manual/pull/67
[1] https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=d3ffd7f77654adafe5f1989bdfdbe4a337ff2e8b
[2] https://github.com/llvm/llvm-project/commit/9e8ed3403c191ab9c4903e8eeb8f732ff8a43cb4