Merge topic 'FindGLUT-pkg-config-HINTS' into release-3.25

a2fc4b6257 FindGLUT: Drop the now-unnecessary exclusion of pkg-config for multiconfig
a60a33dcb0 FindGLUT: Drop the now-unnecessary ALLOW_SYSTEM_CFLAGS logic
4ad57224b5 FindGLUT: Use pkg-config's results as HINTS for normal search

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: Christopher Degawa <cddegawa@gmail.com>
Merge-request: !7770