risc-v: Disable PIC by default for now

risc-v: Disable PIC by default for now

Rust's linker cannot currently handle gcc's fPIC compilation units
for RISC-V targets:

      = note: rust-lld: error:
          .got section detected in the input files. Dynamic relocations are not
          supported. If you are linking to C code compiled using the `gcc` crate
          then modify your build script to compile the C code _without_ the
          -fPIC flag. See the documentation of the `gcc::Config.fpic` method for
          details.

So disable PIC by default for now for `riscv` targets.

Gbp-Pq: Name u-riscv64-cc-430.patch