Default to the medium code model for the loongarch64-linux toolchains

The medium code model is already the default on the Rust side.
Make sure that linked in C objects (e.g. from glibc) also use
medium code model.

Author: heiher

src/ci/docker/host-x86_64/dist-loongarch64-linux/loongarch64-unknown-linux-gnu.defconfig

@@ -7,6 +7,8 @@ CT_ARCH_LOONGARCH=y
 # CT_DEMULTILIB is not set
 CT_ARCH_USE_MMU=y
 CT_ARCH_ARCH="loongarch64"
+CT_TARGET_CFLAGS="-mcmodel=medium"
+CT_TARGET_LDFLAGS="-mcmodel=medium"
 CT_KERNEL_LINUX=y
 CT_LINUX_V_5_19=y
 CT_GLIBC_V_2_36=y

src/ci/docker/host-x86_64/dist-loongarch64-musl/loongarch64-unknown-linux-musl.defconfig

@@ -7,6 +7,8 @@ CT_ARCH_LOONGARCH=y
 # CT_DEMULTILIB is not set
 CT_ARCH_USE_MMU=y
 CT_ARCH_ARCH="loongarch64"
+CT_TARGET_CFLAGS="-mcmodel=medium"
+CT_TARGET_LDFLAGS="-mcmodel=medium"
 CT_KERNEL_LINUX=y
 CT_LINUX_V_5_19=y
 CT_LIBC_MUSL=y