REVIEW-4581: spec updates
REVIEW-4582: spec updates
Spec updates for review items

- Added comment on toolchain configuration after availability check (REVIEW-3196)
- Use Xcode toolchain to determine mac-specific gcc args (REVIEW-3822)
- Clean task for a binary (REVIEW-4104)
- Use Cygwin and MinGW toolchain to build path for installExecutable task (REVIEW-3220)
- Upgrade unknown OS build to run on java 7 so we can test installed executables on unknown os (REVIEW-3150)
- Assembler integration test coverage (REVIEW-3760)
- Support LinkerSpec.libraryPath on GCC (REVIEW-3847)
- Windows libPath test coverage (REVIEW-3847)
REVIEW-3815: Removed separate *NativeBinariesPlugin subclasses
More spec updates for review items

- Changed naming convention for output binaries to use flavor/platform/buildType directories (REVIEW-3194)
- Windows resources linker args (REVIEW-3969, REVIEW-4050)
- Use a model rule to check for resource sources (REVIEW-3971, REVIEW-4017)
REVIEW-3976: Simplify construction of native incremental compiler
REVIEW-3977: Test error message when attempting to compile windows resources with GCC on windows
REVIEW-4014: Use binary.tasks to provide the lifecycle task for a binary.
REVIEW-4061: Re-enable test for building with multiple tool chains in a single build execution