Improve C defined function detection / add C declared variable detection

[ethteck]

We try to do this, but it clearly has some issues as #11 mentions

Conversely, functions defined in C code but non-matching should be disassembled

• Run cpp on c files to figure out which functions are defined
• Improve detection of defined functions
• Add support for detection of declared (non-externed) variables.
• Mark these symbols as defined so they don't get written to undefined_syms_auto

[ethteck]

I don't think detecting defined variables in C code is viable without using pycparser, which is insanely slow. If anyone has other ideas, I'm all ears, but this seems really difficult..

[mkst]

Notes around c function detection:

1. This function will not be detected due to unsigned int being 2 tokens, it is fine if the return type is 1 token, e.g. u32.

unsigned long my_function(int foo) {
    return 0;
}

2. This function will not be detected due to the whitespace between my_function and (int foo).

long my_function (int foo) {
    return 0;
}

I discovered both of these due to me copying the LIBSPU.H definition for a PSX library function, e.g.

extern unsigned long SpuSetNoiseVoice (long on_off, unsigned long voice_bit);