Do not prepend ${prefix} to substituted includedir & libdir
in the pkg-config file -- if the paths are overriden by user, CMake puts
absolute paths there (even if user specifies a relative path). Instead,
use the absolute path provided by CMake and appropriately default
LIBRARY_INSTALL_DIR & INCLUDE_INSTALL_DIR to absolute paths with
${CMAKE_INSTALL_PREFIX} prepended.
Fixes: https://github.com/open-source-parsers/jsoncpp/issues/279
Signed-off-by: Michał Górny <mgorny@gentoo.org>
RPM-based distros such as Fedora or Mageia put 64bit libraries in /usr/lib64
while 32bit libraries go to /usr/lib. This is usually taken into account
in CMake projects using a LIB_SUFFIX parameter that can be set to "" or "64".
