src/meta-openembedded:nlohmann-json: backport gcc10 fix

The following issue and PR describe an issue with nlohmann-json and
GCC10.

nlohmann/json#1920
nlohmann/json#2034

Confirmed that this fixed the issue seen in OpenBMC when pulling in the
latest upstream meta-openembedded.

Signed-off-by: Khem Raj <raj.khem@gmail.com>