On some system (OS X 10.6 was identified as for the address attached), the nepomuk-core fails to compile with the error:
> from [snip]/nepomuk-core/work/nepomuk-core-4.11.1/tools/nepomukctl/main.cpp:39:
> /opt/local/include/QtCore/qthread.h:115: error: declaration does not declare anything

A preprocessor conditional part of code seem to be at fault in this case, in nepomukctl/main.cpp:
> #ifdef __unix__
>     #include <unistd.h>
> #elif defined _WIN32
>     #include <windows.h>
>     static inline void sleep(unsigned int x) { Sleep(1000 * x); };
> #else
>     #define sleep(x)
> #endif

In some OS X systems, testing for __unix__ seems to be unsufficient, so that sleep() is defined at the preprocessor level, conflicting with Qt headers.
A patch provided in the attached URL, which tests for __APPLE__ as well as __unix__, makes it possible to compile the package properly.

Reproducible: Always

Steps to Reproduce:
1. Extract nepomuk-core archive
2. Run cmake with relevant variables
3. Run make
Actual Results:  
The compilation fails with: 
> from [snip]/nepomuk-core/work/nepomuk-core-4.11.1/tools/nepomukctl/main.cpp:39:
> /opt/local/include/QtCore/qthread.h:115: error: declaration does not declare anything


Expected Results:  
The package builds.

The error occurs only on some OS X versions. According to my tests, 10.7 and 10.8 seem to build fine.