XML <extension>: Replace remaining condition with depends

[SunSerega]

Asked at the end of #950. This in particular wasn't answered yet, but after getting a bit more comfortable with new XML - I'm pretty sure this does need to be fixed.

Note: There are also a bunch of <require> tags with condition instead of the depends attribute.
The depends attribute is being used for these too, but only in one place:

            <require depends="CL_VERSION_2_0" comment="From version 0.9.4 of the extension">

But half of the condition attributes here use negation:

            <require condition="!defined(CL_VERSION_1_2)" comment="cl_device_info - defined in CL.h for OpenCL 1.2 and newer">

And there is also one like this:

            <require condition="defined(_WIN32)">

Which is neither a version nor an extension name, so I guess this one cannot be converted to depends?

[bashbaug]

The "conditions" are currently used by the extension header generation scripts:

https://github.com/KhronosGroup/OpenCL-Headers/blob/59452533d2afa817bc2dc0da4f783097f4cdbcb0/scripts/cl_ext.h.mako#L307

I'm OK doing something like this PR to remove redundancy, but we'll need to update the header generation scripts as well if we make this change.

[SunSerega]

Ah, I was somehow sure there were more condition attributes before => most of them were replaced by depends => in-house scripts already work with depends to do the same thing.

[oddhack]

The 'condition' is something OpenCL-specific. The 'depends' was introduced when syncing with the Vulkan scripts and has the same restrictions, it only speaks to extension and core version dependencies.

[SunSerega]

and has the same restrictions

Well, it can represent more cases. For instance in this case:

        <extension name="cl_khr_subgroups" supported="opencl" promotedto="CL_VERSION_2_1" ratified="opencl">
            <require>
                <type name="CL/cl.h"/>
            </require>
            <require condition="!defined(CL_VERSION_2_1)" comment="defined in CL.h for OpenCL 2.1 and newer">
                <type name="cl_kernel_sub_group_info"/>
            </require>
            <require comment="cl_kernel_sub_group_info">
                <enum name="CL_KERNEL_MAX_SUB_GROUP_SIZE_FOR_NDRANGE_KHR"/>
                <enum name="CL_KERNEL_SUB_GROUP_COUNT_FOR_NDRANGE_KHR"/>
            </require>
            <require>
                <command name="clGetKernelSubGroupInfoKHR"/>
            </require>
        </extension>

Here, I don't know how to convert this condition to depends, because of the NOT operator.
But then again, maybe this one doesn't add any new info. Presumably, if an extension is promotedto="CL_VERSION_2_1", then all types it adds should only be defined when CL_VERSION_2_1 is not defined.

But what about all the extensions with depends but not condition - are there cases where generating a macro condition in the header based on depends would be wrong?