CMAKE_INSTALL_LIBDIR can be lib, lib64 or even lib/ on Debian, but we already split the contribs by multiarch-tuple / installation directory at the prefix level for contribs to avoid mixups.
Preventing installation in lib64/ ensure every pc files from contribs/ are in the PKG_CONFIG_PATH when configuring.
Fixes #26888
Cherry-picked from commit 346b2fb9.
Signed-off-by: Alexandre Janniaux ajanni@videolabs.io
VideoLAN code repository instance