Added -C option to request cascading errors. By default, will exit early,
to avoid all error-recovery-based crashes.
This works by simulating end-of-file in input on first error, so no
need for exception handling, or stack unwinding, or any complex error
checking/handling to get out of the stack.
The existing test harness is a homemade shell script. All the tests
and the expected results are written in plain text files. The harness
just reads in a test, invoke the glslangValidator binary on it, and
compare the result with the golden file. All tests are kinda
integration tests.
This patch add Google Test as an external project, which provides a
new harness for reading shader source files, compile to SPIR-V, and
then compare with the expected output.
