Fix clang c++ compiler error in unit tests. (#1027)
Fix clang c++ compiler error in unit tests. (#1027)

Apple's c++ compiler (clang) has issues with array declarations using a
variable.
e.g.
```
error: variable-sized object may not be initialized
```

g++ doesn't seem to have an issue with it.

Some unit tests used this, changing the variable to a constant fixes it.

Fixes #1026
markszabo/IRremoteESP8266,markszabo/IRremoteESP8266,markszabo/IRremoteESP8266,markszabo/IRremoteESP8266