rust-common: Add LDFLAGS to cc wrapper

The -cc wrapper can be used for linking and can fail if key flags are missing:

| error: linking with `[path]/tmp/work/x86_64-linux/rust-native/1.54.0-r0/wrapper/target-rust-cc`

Add the flags to fix builds even if that is counter-intuitive (cc would
normally be used for compiling and ccld for linking).

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>