configure.py: add flag for loongarch64 musl-root

Author: heiher

src/bootstrap/configure.py

@@ -130,6 +130,8 @@ def v(*args):
   "riscv32gc-unknown-linux-musl install directory")
 v("musl-root-riscv64gc", "target.riscv64gc-unknown-linux-musl.musl-root",
   "riscv64gc-unknown-linux-musl install directory")
+v("musl-root-loongarch64", "target.loongarch64-unknown-linux-musl.musl-root",
+  "loongarch64-unknown-linux-musl install directory")
 v("qemu-armhf-rootfs", "target.arm-unknown-linux-gnueabihf.qemu-rootfs",
   "rootfs in qemu testing, you probably don't want to use this")
 v("qemu-aarch64-rootfs", "target.aarch64-unknown-linux-gnu.qemu-rootfs",