Add support for riscv32imac-unknown-xous-elf

The `riscv32imac-unknown-xous-elf` target is a new Tier 3 platform.

Signed-off-by: Sean Cross <[email protected]>

Author: xobs

src/lib.rs

@@ -2694,6 +2694,11 @@ impl Build {
                 "riscv64-unknown-elf",
                 "riscv-none-embed",
             ]),
+            "riscv32imac-unknown-xous-elf" => self.find_working_gnu_prefix(&[
+                "riscv32-unknown-elf",
+                "riscv64-unknown-elf",
+                "riscv-none-embed",
+            ]),
             "riscv32imc-unknown-none-elf" => self.find_working_gnu_prefix(&[
                 "riscv32-unknown-elf",
                 "riscv64-unknown-elf",