Supplementing compiler tests suite with coverage for missing macro features

The shortages were spotted around `test_opencl_c_versions.cpp` and `test_feature_macro.cpp` source files. Missing coverage refers to:

-`__opencl_c_integer_dot_product_input_4x8bit_packed`
-`__opencl_c_integer_dot_product_input_4x8bit`
-`__opencl_c_kernel_clock_scope_device`
-`__opencl_c_kernel_clock_scope_work_group`
-`__opencl_c_kernel_clock_scope_sub_group`

Start by reading test_opencl_c_versions.cpp and test_feature_macro.cpp to understand how existing feature-macro coverage is structured. Add coverage for the five listed OpenCL C macros, then run the relevant compiler test suite and confirm each macro is exercised.

Written by the indexing model from the issue text.