Some small changes to the CPP-bits of eval.c

[Rewbert]

I am compiling for a target (STM32L552) where I have this set of configs

#define WANT_STDIO 1
#define WANT_FLOAT32 1
#define WANT_MD5 0
#define WANT_TICK 0
#define WANT_ARGS 0
#define GCRED    0
#define FASTTAGS 1
#define INTTABLE 1
#define SANITY   1
#define STACKOVL 1

#define HEAP_CELLS 8000
#define STACK_SIZE 500

and there were some errors to take care of before compiling could proceed. I have executed make everytest without problem before opening this MR, but I don't yet know how these changes affect the other build targets (I guess CI will tell us).

There are two other problems that arises from this set of configurations, but I will open an issue describing them shortly, and we'll see what you want to do.

[augustss]

Maybe we need WANT_UNISTD?
I don't remember exactly what's used from unistd.h

[Rewbert]

The only thing I noticed was unlink, because with the current set of flags it did not work. For my specific platform I don't think I need unistd, so a guard that chucks away the entire thing works well for me lol.

[augustss]

I think you should make a config for this target and include it in CI.
It's a good mix of features when dealing with microcontrollers.