PRI* macros not defined for VxWorks

[kevin-f-ortega]

F´ Version	55c199d4ddeffdce15c2d4e446c156954770aa3e
Affected Component	VxWorks 7.0

---

Problem Description

Receive several of these errors when compiling for VxWorks 7.0

~/fprime/Fw/Types/PolyType.cpp: In member function 'void Fw::PolyType::toString(Fw::StringBase&, bool) const':
~/fprime/Fw/Types/PolyType.cpp:617:66: error: expected ')' before 'PRIu8'
                 (void) snprintf(valString, sizeof(valString), "%" PRIu8 " ", this->m_val.u8Val);
                                ~                                 ^~~~~~
                                                                  )

How to Reproduce

1. Compile for VxWorks 7.0

Expected Behavior

Compile without these errors.

[kevin-f-ortega]

Addressed in https://github.com/nasa/fprime/pull/1434