wsi: suppress "unused function" warning

Several of these types are only converted one way.
Instead of splitting these into multiple macros, let's just `MAYBE_UNUSED` them.

Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
15 jobs for !584 with wsi-unused-function-warning in 15 minutes and 56 seconds (queued for 2 seconds)
detached
Status Job ID Name Coverage
  Containers Build
passed #216858
ubuntu

00:00:46

 
  Build+Test
passed #216859
autotools

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passed #216861
meson-clang

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passed #216867
meson-gallium-clover-llvm

00:01:56

passed #216868
meson-gallium-clover-llvm39

00:01:26

passed #216866
meson-gallium-drivers-other

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passed #216865
meson-gallium-radeonsi

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passed #216869
meson-gallium-st-other

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passed #216860
meson-gallium-swr

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passed #216864
meson-glvnd

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passed #216863
meson-loader-classic-dri

00:08:06

passed #216862
meson-vulkan

00:03:01

passed #216871
scons-llvm

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passed #216870
scons-nollvm

00:03:37

passed #216872
scons-swr

00:06:55