Add more standard includes

[niels-moller]

I'm not sure what's the recommended way is to use the header files in tkey-libs. To me, it makes most sense to use -I .../tkey-libs/include when compiling apps and libraries for the tkey. Then tkey-specific headers can be used as #include <tkey/debug.h>.

That makes the top-level tkey-libs/include directory a reasonable place for standard C include files that aren't provided by the compiler. I'm missing at least assert.h (which could either just include tkey/assert.h, or have the latter file move up one level), stdlib.h (which at a minimum should declare abort ()), and string.h which should declare standard functions now in tkey/lib.h, as well as additional utilities that are currently missing, e.g., memcmp and strcmp.

Is this a reasonable approach, or do you see a better place for the standard C includes that are currently missing?

One might consider splitting libcommon into one library that is essentially a libc subset, and one library with tkey-specific utilities, but to me it seems good enough to have it all in libcommon.

Related to #51.

[mchack-work]

I think it would make sense to use some existing BSD-licensed libc and make sure that works for TKey.

[niels-moller]

For <string.h>, see #84. After that, I'd like to see <assert.h> and <stdlib.h>.

In addition, I've also had to hack around missing <stdio.h>, <ctype.h> and <time.h>, but for those it's not clear to me if it makes sense for tkey-libs to provide them.

[mchack-work]

Any ideas if porting newlib, musl, or embedded artistry's libc to TKey might be a better idea? I mean, re-implementing the entire libc. Again! What would be a good fit? musl explicity mentions RV32.

We could keep just the TKey specific stuff in tkey-libs and port one of the existing libc's.

[niels-moller]

We could keep just the TKey specific stuff in tkey-libs and port one of the existing libc's.

In principle, sounds great. But I have no idea how practical it is, and which libc would be a good fit. E.g., does it make any sense to have all stdio functions?

And regarding assert.h and stdlib.h (including the abort() call), that's going to be tkey specific, just reusing some "portable" implementation won't work without some tweaks.