phrasing for OpenCL C extension requirements

I've noticed a handful of small issues or possibilities for improvemnent how the OpenCL C specification describes dependencies on OpenCL extensions:

1. The descriptions for the integer dot product functions dot etc. have a line that ends in a comma, for example:

> Requires that the __opencl_c_integer_dot_product_input_4x8bit feature macro is defined,

We should figure out whether something else needs to be said here or change the comma to a period.

2. Other extensions use phrasing similar to:

> Double-precision floating-point is supported if the cl_khr_fp64 extension macro is supported [...]

In sentences like these do we want to call out the extension macro specifically or should we refer to the extension generally instead, something like "if the cl_khr_fp64_extension is supported"? This shouldn't really matter in practice, since the extension macro will be defined when the extension is supported, but I personally find it more understandable to refer to the extension and not the macro. Note, even if we decide to keep the extension macro text, we may want to say "if the extension macro is defined" rather than "supported".

Start by reviewing the OpenCL C specification passages for integer dot product functions and the cited extension requirements. Decide whether the incomplete comma-ending text and macro terminology should be revised, then apply the chosen wording consistently across the affected documentation and verify that all referenced requirements remain accurate.

Written by the indexing model from the issue text.