Allow the S2N_NO_PQ environment variable to set the correct build fla…

…g. (aws#1968)

* Allow the S2N_NO_PQ environment variable to set the correct build flag.
Update tests to run depending on this flag.
* Change character type to detect ARM EOF.
Update kem function to use ENSURE_POSIX macros.
* Fix Makefile typo

Release 0.10.3

Release 0.10.2

Test branch as of 10 Mar 2020

Release v0.10.1

Release 0.10.0