I copied the constants and definitions from musl which we can presume is
correct. Relibc is missing some features which affects our sysconf as
well, such as constants in limits.h or a working resources.h.
Also make fields in `termios` public; required for modifying them.
There's an new type of test: `EXPECT_INPUT_BINS`. These require a `.exp`
file to be present along with the `.c` file. The `.exp` file takes the
produced binary as an argument and sends input to the program. This is
useful for testing functions like `getpass()`.
Jeremy Soller