Merge pull request #1305 from Xeonacid/patch-1

Set fast_arithmetic=64 for riscv64

Author: dtolnay

build.rs

@@ -13,6 +13,7 @@ fn main() {
  || target_arch == "loongarch64"
  || target_arch == "mips64"
  || target_arch == "powerpc64"
+ || target_arch == "riscv64"
  || target_arch == "wasm32"
  || target_arch == "x86_64"
  || target_pointer_width == "64"