Definition of 'null' in sc_types.h clashes with alternative definitions especially in C++

[terfloth]

There are some problems with the definition of 'null' in sc_types.h in the context of C++:

• it does not make use of existing C++ definitions
• 'null' is likely subject to definition clashes. As an example Qt 5.10 upwards also defines that symbol.

Additionally the literal name is defined by a constant and thus is not easily changeable for platform specific code generators.

So the following actions must be taken

• replace the 'null' by 'sc_null'
• redefine sc_null in sc_types.h for C
• redefine sc_null sc_types.h for C++ to be 'NULL'
• replace constant by extension method in C & C++ code generators