Setting this to an empty string will result in the kernel invoking just "ld" for linking, rather than aarch64-alpine-linux-musl-ld. When building with GCC and linking with BFD, we still need to rely on pmbootstrap to set CROSS_COMPILE appropriately, overriding it will break cross compilation. Part-of: <https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/8622>