If you update the kernel headers tarball and run make against an already built

buildroot, the header files will be re-extracted, but they will not be put in
exactly the right place if the name of the extracted directory includes the
kernel version numbers.

For example, linux-libc-headers-2.4.25.tar.bz2 will be extracted to
$(TOOLCHAIN_BUILD_DIR)/linux-libc-headers-2.4.25, and then the mv command will
move the newly extracted headers into the already existing
$(TOOLCHAIN_BUILD_DIR)/linux directory, instead of replacing that directory as
desired.

The fix is to first remove the $(TOOLCHAIN_BUILD_DIR)/linux directory and then
do the mv command.

http://bugs.busybox.net/view.php?id=296