CMakeLists.txt and doc changes for
1) Ninja build and QTCreator IDE support
2) Out of tree builds that aren't based on using update_external_sources and build_windows_target scripts
3) Allowing the developer to use non-default locations for glslang and SPIRV-Tools binaries and sources
4) Fix linux build when developer chooses not to rename SPIRV-Tools to spirv-tools

Change-Id: Ib6118c47dc780e6721ec0538aae1a6ee444eed78
4 files changed