linux-yocto-all: add sysroot native include path for gcc plugin build

For qemuarm  builds we have seen the case that ths gcc plugins build
inside the linux kernel has been failing on missing header files gmp.h,
mcp.h and others. The native dependencies have been available, but the
kernel Makefile did not have the correct include path for the headers.

Neither poky dunfell nor master has this problem. No upstreaming needed.

Closes: https://git.ostc-eu.org/OSTC/OHOS/meta-ohos/-/merge_requests/93



Signed-off-by: Stefan Schmidt <stefan.schmidt@huawei.com>