Fix CPPCheck Issues - Member function can be static

[eljonny]

These CPPCheck issues need to be investigated - and possibly corrected (they are in the inconclusive sub-category)

include/internal/TestCPPTestCase.h:199:14: performance: inconclusive: Technically the member function 'TestCPP::TestCase::clearStdoutCapture' can be static (but you may consider moving to unnamed namespace). [functionStatic]
        void clearStdoutCapture ();
             ^
src/TestCPPTestCase.cpp:461:20: note: Technically the member function 'TestCPP::TestCase::clearStdoutCapture' can be static (but you may consider moving to unnamed namespace).
    void TestCase::clearStdoutCapture () {
                   ^
include/internal/TestCPPTestCase.h:199:14: note: Technically the member function 'TestCPP::TestCase::clearStdoutCapture' can be static (but you may consider moving to unnamed namespace).
        void clearStdoutCapture ();
             ^
include/internal/TestCPPTestCase.h:207:14: performance: inconclusive: Technically the member function 'TestCPP::TestCase::clearLogCapture' can be static (but you may consider moving to unnamed namespace). [functionStatic]
        void clearLogCapture ();
             ^
src/TestCPPTestCase.cpp:467:20: note: Technically the member function 'TestCPP::TestCase::clearLogCapture' can be static (but you may consider moving to unnamed namespace).
    void TestCase::clearLogCapture () {
                   ^
include/internal/TestCPPTestCase.h:207:14: note: Technically the member function 'TestCPP::TestCase::clearLogCapture' can be static (but you may consider moving to unnamed namespace).
        void clearLogCapture ();
             ^
include/internal/TestCPPTestCase.h:215:14: performance: inconclusive: Technically the member function 'TestCPP::TestCase::clearStderrCapture' can be static (but you may consider moving to unnamed namespace). [functionStatic]
        void clearStderrCapture ();
             ^
src/TestCPPTestCase.cpp:473:20: note: Technically the member function 'TestCPP::TestCase::clearStderrCapture' can be static (but you may consider moving to unnamed namespace).
    void TestCase::clearStderrCapture () {
                   ^
include/internal/TestCPPTestCase.h:215:14: note: Technically the member function 'TestCPP::TestCase::clearStderrCapture' can be static (but you may consider moving to unnamed namespace).
        void clearStderrCapture ();
             ^
include/internal/TestCPPTestSuite.h:117:16: performance: inconclusive: Technically the member function 'TestCPP::TestSuite::addTests' can be static (but you may consider moving to unnamed namespace). [functionStatic]
        inline addTests () { }
               ^