Variable definition in usm.hpp conflicts with user macro

[Pennycook]

#5391 introduced several variables called "CL", for example here:

llvm/sycl/include/CL/sycl/usm.hpp

Lines 21 to 23 in 708a5bf

	__SYCL_EXPORT void *malloc_device(
	size_t size, const device &dev, const context &ctxt,
	const detail::code_location CL = detail::code_location::current());

This conflicts with a "CL" macro in an application I'm working on. Can we change all of these to loc or codeLoc instead?

It might also be a good idea to add some sort of check for variable names in caps to prevent this sort of thing.