Separating file I/O from compile/link lets the compile/link be done
repeatedly in a loop for testing and measuring of performance and
memory footprint, including seeing memory growth over time for
functional-level memory-leak testing.
While the older compile-only mode already had this functionality,
and typically showed no memory leaks, SPIR-V uses the link path,
has pending "TODO" for memory freeing, and this shows several
kilobytes of leaking per compile-link. Most likely, pending
merge request 131 will address much of this.
Using platform-neutral osinclude.h makes it easier to substitute
implementation when necessary and eliminates some variability between
build configurations.
