gcc has an option -isystem, that can replace -I. The documentation is:
-isystem dir
Search dir for header files, after all directories specified by -I but
before the standard system directories. Mark it as a system directory,
so that it gets the same special treatment as is applied to the
standard system directories. If dir begins with "=", then the "=" will
be replaced by the sysroot prefix; see --sysroot and -isysroot.
The "special treatment" means that gcc will not warn about constructions in
headers in directories pointed by -isystem instead of -I.
In the CGAL testsuite, there are a lot of warnings that comes from
third-party libraries (mostly from Boost, but also from Eigen).
This patch tells cmake to use -isystem with gcc, for all CGAL 3rd-party
directories.
Laurent Rineau
Sébastien Loriot