These make cross compiling the test suite more difficult, as you need
the
sysroot to contain these headers and libraries cross compiled for your
target.
It's straightforward to stick with the corresponding C headers.
This patch increases the timeout of the libc test from 1s to 10s, mostly because rv32 runs in a qemu image and sometimes 1s is just not enough for the test to finish when there are other tests running in parallel
A convenience wrapper name `add_libc_test` is also added which adds both
a unit test and a hermetic test. The ctype tests have been switched over
to use add_libc_test.
Reviewed By: jhuber6
Differential Revision: https://reviews.llvm.org/D148756
