package/wampcc: fix build failure on RISC-V/musl

package/wampcc: fix build failure on RISC-V/musl

wampcc includes some code from msgpack-c, which itself includes some
code from Boost for the endianness detection. This code did not
properly handle the case of the RISC-V architecture supported by
non-glibc toolchains, causing the endianness to be unknown (and a
build failure) when building wampcc for RISC-V with the musl C
library.

This commit fixes that, by bringing a change that was upstreamed to
Boost as of commit
https://github.com/boostorg/predef/commit/4bc7cc02eda854e4c8ac73caecfee37717083a6b.

Fixes:

  http://autobuild.buildroot.net/results/01df5a6f38fb32563831d171d03dfb9ad89f5830/

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