Fix out-of-tree build of libelf
Fix out-of-tree build of libelf

native-elf-format.h is auto-generated in the build tree
but only the source tree was on the include path.

Repro steps: "cd build_dir && $(SRC_DIR)/configure && make"

Open343/pkg,khorben/pkg,skoef/pkg,en90/pkg,Open343/pkg,en90/pkg,skoef/pkg,junovitch/pkg,junovitch/pkg,khorben/pkg,khorben/pkg