make a proper symbolic libc

[zapashcanon]

we should provide a libc where all functions are returning proper symbolic values, this would help in identifying bugs in more real-world code

[filipeom]

Frederico was working on something similar: https://github.com/frediramos/LibcSummaries

I don't know the current state of the project. But, our libc was a very early version of his work which I extended with a bunch of dietlibc's function just to be able to compile some of the benchmarks in aws-encryption-sdk-c

[zapashcanon]

It seems the repository is private and I can't access it unfortunately