Port Benchmarks to C with Boehm GC

[smarr]

Main challenge are the few polymorphic elements for instance in DeltaBlue.

[rochus-keller]

In case you're intereseted: here is a native version of the benchmark suite in C with conventional memory management (i.e. not using Boehm): https://github.com/rochus-keller/Are-we-fast-yet/tree/main/C.

The performance is very close to my C++ version (about 2% slower).

Concerning the postulated C version with Boehm: not sure if you are aware that my Oberon+ has a C99 transpiler which can generate a C99 version of my Oberon+ Are-we-fast-yet version using Boehm; here is the generated source code: http://software.rochus-keller.ch/awfy_c99_benchmark.tar.gz. I compared it with the forementioned native C99 version, with the latter only ~20% faster.