Don't buffer test output (#633)
Don't buffer test output (#633)

When using `cmake --build <PATH> --target check-spirv`, print the tests
output directly to the console instead of waiting for all the tests to
have finished to print everything in bulk. Tested with Ninja.

Signed-off-by: Marco Antognini <22c7c6a125704d89f5288f7df787c63bc5928de6@arm.com>
google/clspv,google/clspv,google/clspv,google/clspv,google/clspv