A few fixes/additions to translate-c

• Undefined C variables now get initialized to undefined in Zig.
• If statements on floats and ints in C, are now translated to working Zig code. The code generated seems to be the simplest code, that both handles ints and floats. Sadly, this doesn't work on nullable pointers (or pointers, but every pointer becomes nullable in translation).

I can see, that translate_c puts ; behind every statement. This is actually not always valid in Zig.

test "" {
    // error: invalid token: ';'
    if (true) { };
}

I was considering making translate_c only sometimes output semicolon, but I didn't actually know if Zig is supposed to accept the use case above (All tests a written with the semicolon, so maybe it's supposed to work?)