glx: Check for byte-swapping in SetReplyHeader

Check for the need to byte-swap when attempting to display
GL apps between a big-endian server and little-endian client
or vice versa.

Fixes: xorg/xserver#1127
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00:00:12

 
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00:04:42

passed meson #10264140

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passed meson-noglamor #10264141

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passed mingw-cross-build #10264142

00:01:11