Fix all compile warnings

[imbillow]

Your checklist for this pull request

• I've read the guidelines for contributing to this repository
• I made sure to follow the project's coding style
• I've documented or updated the documentation of every function and struct this PR changes. If not so I've explained why.
• I've added tests that prove my fix is effective or that my feature works (if possible)
• I've updated the rizin book with the relevant information (if needed)

Detailed description

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Test plan

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Closing issues

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[wargio]

../librz/bin/filter.c:9:13: error: variable ‘bo’ set but not used [-Werror=unused-but-set-variable]
    9 |         ut8 bo[0x100];

[XVilka]

../librz/bin/filter.c
../librz/bin/filter.c: In function ‘false_positive’:
../librz/bin/filter.c:9:13: error: variable ‘bo’ set but not used [-Werror=unused-but-set-variable]
    9 |         ut8 bo[0x100];
      |             ^~
cc1: all warnings being treated as errors

Also, these are imported from binutils and will be eventually migrated to Capstone:

• librz/asm/arch/arc/gnu/*
• librz/asm/arch/lanai/gnu/*
• librz/asm/arch/tricore/gnu/* by you

Probably better not to change them, if it doesn't affect CI: #2704

If it does affect CI, then it's fine to change them too, just keep in mind that eventually we hope to remove these files completely.