We remove the shared library compile/link flags "-fPIC" and "-shared"
because they are not provided by all compilers on Linux. This allows us
to drop code from the Linux-XL-*.cmake files that erases the bad flags.
All other supported compilers already provide their correct flags for
Linux in their own platform information files.
This is a GNU-specific option that should not be specified for all
compilers on Linux. It tells the GNU compiler to pass -export-dynamic
to the linker to export symbols from executables for use by plugins.
Since we provide the ENABLE_EXPORTS target property to do the same thing
in a cross-platform way, there is no need to pass -rdynamic always.
Since the option is not useful for GNU tools and breaks other tools on
Linux we simply remove it from CMAKE_SHARED_LIBRARY_LINK_<lang>_FLAGS.
This also allows us to stop setting the variable in other Linux compiler
files just to erase the bad flag.
See issue #9985.
IBM rebranded its VisualAge compiler to XL starting at version 8.0. We
use the compiler id "XL" for newer versions and "VisualAge" for older
versions. We now also recognize the "z/OS" compiler, which is distinct
from XL.
