package/boost: fix RISC-V musl endian detection

package/boost: fix RISC-V musl endian detection

The recent addition of a RISC-V musl toolchain uncovered an issue in
Boost's endianness detection. Boost endianness detection only works
for C libraries that pretend to be glibc *or* if the architecture is
explicitly handled by Boost endian.h header. Neither were true for
RISC-V musl, so we slightly patch boost to fix this problem.

Fixes:

  http://autobuild.buildroot.net/results/a40b600a7d0fdb6a8a1ded7883b4936f120811f5/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>