CHICKEN benchmarks -- patches by megane

Notes

Benchmarks executed on Debian GNU/Linux 10 considering the following variants:
- hardware architectures: x86 and x86-64
- C compilers: GCC 8.3.0 and clang 7.0.1
- benchmark programs: from chicken-benchmarks and chicken-benchmarks-extra
- CHICKEN build options: default and OPTIMIZE_FOR_SPEED=1
- CHICKEN: master as of 6bca0f85756b240cb5038608761f68573ffa9241 (patches by megane on top of that)
Differences in the representation of results (e.g. numerical results that look the same but are presented in different font color or bar length) are caused by rounding
Raw logs

Note: base64 from chicken-benchmarks-extra fails on x86 because that benchmark program uses large strings and the base64 egg uses fixnums.