Use low level non-blocking I/O for process pipe streams. This may fix issues with data not getting through the pipe occasionally.
Related: https://github.com/libsdl-org/SDL/issues/11006
We require stdbool.h in the build environment, so we might as well use the plain bool type.
If your environment doesn't have stdbool.h, this simple replacement will suffice:
typedef signed char bool;
Also marked the existing functions as unsafe, as they can cause crashes if used in multi-threaded applications.
As a bonus, since the new functions are hashtable based, hint environment lookups are much faster.
