Path.Combine(ModuleDirectory, "../../ThirdParty/glm")
Yes, Unreal build system does not build the ThirdParty libraries, as it is usually intended to build them outside, or download a built package, and include the shared libraries.
Alternatively, you could do something like that:
MyLibrary.cpp
#include "MyLibraryHeader.h"
#include "MyProject.h" // the required precompiled header
#include "MyLibraryCode_1.cpp"
#include "MyLibraryCode_2.cpp"
...