Add wtf_unittests target that links unit tests outside DLL

Source/wtf/wtf.gypi

 {
     'variables': {
         'wtf_files': [
             'ASCIICType.h',
             'AVLTree.h',
             'Alignment.h',
             'ArrayBuffer.cpp',
             'ArrayBuffer.h',
             'ArrayBufferContents.cpp',
             'ArrayBufferContents.h',
@@ skipping 225 matching lines @@
             'tests/SaturatedArithmeticOperations.cpp',
             'tests/StringBuilder.cpp',
             'tests/StringHasher.cpp',
             'tests/StringImpl.cpp',
             'tests/StringOperators.cpp',
             'tests/TemporaryChange.cpp',
             'tests/Vector.cpp',
             'tests/VectorBasic.cpp',
             'tests/VectorReverse.cpp',
             'tests/WTFString.cpp',
+            'tests/RunAllTests.cpp',
         ],
     },
 }