compiler note about ABI being changed in GCC 4.6

[RABijl]

when using a cl_ulong4, the following compiler note shows up:

/home/rabijl/Projects/pocl-2/pocld/../include/hpp/CL/opencl.hpp: In member function ‘cl_int cl::CommandQueue::enqueueFillBuffer(const cl::Buffer&, PatternType, cl::size_type, cl::size_type, cl::vector<cl::Event>*, cl::Event*) const [with PatternType = cl_ulong4]’:
/home/rabijl/Projects/pocl-2/pocld/../include/hpp/CL/opencl.hpp:7679:12: note: the ABI for passing parameters with 32-byte alignment has changed in GCC 4.6
 7679 |     cl_int enqueueFillBuffer(
      |            ^~~~~~~~~~~~~~~~~

[bashbaug]

Interesting, here's a shorter version of this issue: https://godbolt.org/z/67arzdq5a

We removed the alignment information from the scalar OpenCL types a very long time ago (see KhronosGroup/OpenCL-Headers#40), but we didn't remove the alignment information from the vector types. I wonder if that was a mistake. Removing __attribute__ ((aligned(_x))) will fix this warning.

[RABijl]

I played around a bit with the short version and I notice that it does not complain if the alignment is set from 32 to 16 or if it is compiled with some form of -mavx. I don't know if the complexity added by checking for x86 (the arm and risc-v gcc compilers did not show any notes) and a whitelisted set of extension attributes (link) is worth the effort, but I could make make a pr like that and test it against godbolt.

edit: this does the trick: https://godbolt.org/z/714ofrPjh