Programs and libraries using compiler and system information about
endianness often include the system header `<endian.h>`.
In `xtensa-gcc` compiler with `newlib` distribution, that file is located in
`<machine/endian.h>`; this means that `#include <endian.h>` would fail
at compile time.
This commit fixes the issue by adding a compatibility `<endian.h>`
header which in turn just includes `<machine/endian.h>`.
Signed-off-by: Francesco Giancane <francesco.giancane@accenture.com>
Merges https://github.com/espressif/esp-idf/pull/4784
