Add support for scons build system

Infer 0.16
Ubuntu 19.04

When I try to execute command `/home/rafal/Pobrane/infer-linux64-v0.16.0/bin/infer run -- scons p=x11 -j6`, then this errors occurs
```
Usage Error: Unsupported build command 'scons'.
If this is an alias for another build system that infer supports, you can use
`--force-integration ` where is one of the following supported build systems:
ant
buck
cc
gradle
java
javac
make
mvn
ndk-build
xcodebuild
```

Project which I wanted to check is Godot Engine
Github - https://github.com/godotengine/godot
Docs how to compile - https://godot.readthedocs.io/en/3.1/development/compiling/compiling_for_x11.html