Fix incorrect LD/TARGET_LD env vars

The env vars LD and TARGET_LD are exported, but incorrectly refer to a script that doesn't exist (probably a typo). Fix the typo to refer to the proper scripts.

Fixes rust-embedded#128

Author: rich-g

classes/cargo.bbclass

@@ -116,8 +116,8 @@ cargo_do_compile() {
     export TARGET_CXX="${WRAPPER_DIR}/cxx-wrapper.sh"
     export CC="${WRAPPER_DIR}/cc-native-wrapper.sh"
     export CXX="${WRAPPER_DIR}/cxx-native-wrapper.sh"
-    export TARGET_LD="${WRAPPER_DIR}/ld-wrapper.sh"
-    export LD="${WRAPPER_DIR}/ld-native-wrapper.sh"
+    export TARGET_LD="${WRAPPER_DIR}/linker-wrapper.sh"
+    export LD="${WRAPPER_DIR}/linker-native-wrapper.sh"
     export PKG_CONFIG_ALLOW_CROSS="1"
     export LDFLAGS=""
     export RUSTFLAGS="${RUSTFLAGS}"