tools/build-manifest: Add support for RISC-V 32-bit

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

Author: alistair23

src/tools/build-manifest/src/main.rs

@@ -110,6 +110,7 @@ static TARGETS: &[&str] = &[
     "riscv32i-unknown-none-elf",
     "riscv32imc-unknown-none-elf",
     "riscv32imac-unknown-none-elf",
+    "riscv32gc-unknown-linux-gnu",
     "riscv64imac-unknown-none-elf",
     "riscv64gc-unknown-none-elf",
     "riscv64gc-unknown-linux-gnu",