Improve libgdiplus path handling
Since libgdiplus is not installed together with Mono, it should not be
assumed to be in the same prefix.
The new policy for the --with-libgdiplus configure option is the
following:
- --with-libgdiplus=/absolute/path/to/libgdiplus.{so,dylib}
both during build/check and after installation Mono will try to use
the specified libgdiplus library; the rationale is that when an
absolute path is given, it can be assumed to be the full path to
the library that is already installed (possibly in a non-default
path).
- default, --with-libgdiplus=no, --with-libgdiplus=installed
both during build/check and after installation Mono will try to use
a system-wide libgdiplus library, that is assumed to reside in the
paths that are automatically searched by the dynamic linker; the
library is supposed to be already installed in the default path and
to be useable both during the build and afterwards.
- --with-libgdiplus=sibling, --with-libgdiplus=yes
during build/check Mono will try to use the libgdiplus library that
is assumed to be in the sibling folder (../libgdiplus), but after
the installation it will try to use a system-wide libgdiplus
library, that should be in the paths that are automatically
searched by the dynamic linker; the assumption is that the library
is not yet installed, but it will go to the default prefix after
installing it.
- --with-libgdiplus=../some/relative/path/to/libgdiplus.{so,dylib,la}
during build/check Mono will try to use the specified libgdiplus
library, but after the installation it will try to use a
system-wide libgdiplus library, that should be in the paths that
are automatically searched by the dynamic linker; the assumption is
that the library is not yet installed, but it will go to the
default prefix after installing it.