st/nir: Don't use GLSL IR's MOD_TO_FLOOR lowering if nir_lower_dmod set

Both GLSL IR and NIR perform the same mod -> floor lowering for 32-bit
types.  But nir_lower_double_ops is slightly more defensive against
lowered drcp precision loss, and handles mod(x, x) = 0 directly.  This
works well...assuming nir_lower_double_ops actually gets an fmod op to
lower in the first place.

If drivers have requested dmod lowering, assume they're doing all their
fmod handling in NIR and shut off the GLSL IR pass.  Apparently iris is
the only driver requesting dmod lowering today.

Fixes KHR-GL45.gpu_shader_fp64.builtin.mod_dvec[234] on iris.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
10 jobs for !904 with iris-dmod in 9 minutes and 51 seconds (queued for 1 second)
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debian

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meson-clang

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meson-clover

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meson-main

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meson-swr-glvnd

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meson-vulkan

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scons-llvm

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scons-nollvm

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scons-swr

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scons-win64

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