When running on MacOS, undefine __BLOCKS__ in the preprocessor flags of the C++ parser.

We don't support blocks yet, and this way we get rid of quite some
parsing errors (resulting in undefined or wrongly defined types, messing
up the semantic passes).

Reviewed-by: Roberto Raggi

src/plugins/projectexplorer/toolchain.cpp

@@ -174,6 +174,14 @@ QByteArray GccToolChain::predefinedMacros()
         cpp.closeWriteChannel();
         cpp.waitForFinished();
         m_predefinedMacros = cpp.readAllStandardOutput();
+
+#ifdef Q_OS_MAC
+        int idx = m_predefinedMacros.indexOf("#define __BLOCKS__ 1");
+        if (idx != -1) {
+            idx = m_predefinedMacros.indexOf("1", idx);
+            m_predefinedMacros[idx] = '0';
+        }
+#endif // Q_OS_MAC
     }
     return m_predefinedMacros;
 }