FreeBSD 13.2 compilation error.

[tmcgilchrist]

Short description is that hdr_endian.h doesn't expand correctly on FreeBSD resulting in these kinds of errors:

In file included from /src/_build/default/lib/libhdr_histogram/src/hdr_histogram_log.c:33:
/src/_build/default/lib/libhdr_histogram/src/hdr_endian.h:51:10: warning: 'be16toh' macro redefined [-Wmacro-redefined]
#       define be16toh(x) betoh16(x)
               ^
/usr/include/sys/_endian.h:111:9: note: previous definition is here
#define be16toh(x)      __bswap16((x))
        ^
In file included from /src/_build/default/lib/libhdr_histogram/src/hdr_histogram_log.c:33:
/src/_build/default/lib/libhdr_histogram/src/hdr_endian.h:52:10: warning: 'le16toh' macro redefined [-Wmacro-redefined]
#       define le16toh(x) letoh16(x)
               ^
/usr/include/sys/_endian.h:114:9: note: previous definition is here
#define le16toh(x)      ((uint16_t)(x))
        ^
In file included from /src/_build/default/lib/libhdr_histogram/src/hdr_histogram_log.c:33:

Full compile error ocaml-multicore/hdr_histogram_ocaml#6 with fixes available on ocaml-multicore/hdr_histogram_ocaml#7