When crosscompiling, we need to search for the linux kernel headers in the sysroot but since #97486 the linux kernel headers were always searched in /usr/include.
This patch fixes this behaviour by prepending a '=' to where we search for the kernel headers. As per the gcc/clang's documentation a '=' before the path is replaced by the sysroot.
This patch also includes a fix for rv32, that fails to compile due to a missing definition of CLOCK_REALTIME after this change.
ac11430983