Improve EUR address handling

[Kewlan]

• Combine linker scripts

Pass _EUR_ to linker script when building EUR patch and use built-in function DEFINED to determine the address.

• Use macro for game addresses in C code

Takes the USA address and when building for EUR, adds the necessary offset.
I decided to wrap all references to game addresses in it, and also remove the *_addr defines for consistency.

[HylianFreddy]

Good job on this, I just have a couple of suggestions/changes which I put in the comments (and also on this branch if you prefer: https://github.com/HylianFreddy/OoT3D_Randomizer/commits/region-addr)

I also have a question, should all base game addresses be wrapped within the macro? Some still aren't, but it doesn't really change anything so it's fine either way.
I found 43 with this regex: \)0x[a-f,A-F,0-9]{6}

[Kewlan]

@HylianFreddy Excellent suggestions! And thanks for the commits!