"key" was not declared in this scope

[Nashman222]

I got a small error that is preventing me from building:
bullet3/src/LinearMath/btSerializer.h:202:42: error: 'key' was not declared in this scope

There error is in reference to the line
const int* valuePtr = mTypeLookup.find(key);

The line right before that one is:
btHashString key(type);

So key is definitely declared in that scope,
funny enough it does compile fine if I change the name to key1.

This error also didn't show up until I included btBulletDynamicsCommon.h in my project and a libLinearMath.a seems to build ok without any changes.

Currently tested on two computers running Linux using gcc 9.3
Seems to still happen on the latest version pulled from master aswell