This effects 4.x, where int/uint conversions are done, but not earlier.

Fix #137 by avoiding a C++11 feature.

SPV: Split loop header from condition testing for for/while loops.

Apparently, older MSVC versions don't support brace-initializers for
function arguments.

Thanks @baldurk for a suggestion on his branch.

SPV: Don't remove SPIR-V blocks before codegen, use new InReadableOrder instead.

A removed block releases its instructions, so Module::idToInstruction
suddenly contains dangling references.  The original motivation for
block removal was to skip some unreachable blocks, but that's already
achieved by InReadableOrder.cpp.

Also updated stale comments.

SPV: Rework loop code generation to match SPIR-V 1.0.

SPV: Code-generate SPIR-V blocks in a more readable order

Add a test for unreachable merge block.

Update test results with the new order: mainly delaying merge blocks and
removing unreachable ones.

Freed up some command line memory (not used programmatically).

Free memory associated with SPIR-V generation and the pragmaTable.

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.

Parser & SPV: Implement two extensions regarding GLSL sparse texture.