Test cl_ext_cxx_for_opencl (#1095)

Add tests for API extension for compilation
of kernels in C++ for OpenCL language.
* Test that -cl-std=CLC++ is accepted and a
  basic kernel with C++ features is compiled.
* Test that API extension reports the same
  language version as __OPENCL_CPP_VERSION__.

This commit also adds a separate folder for extension
tests.

Signed-off-by: Victoria Holodovsky <victoria.holodovsky@arm.com>

Co-authored-by: Victoria Holodovsky <victoria.holodovsky@arm.com>
7 files changed