link-warning-as-error

• The CMAKE_LINK_WARNING_AS_ERROR variable and corresponding LINK_WARNING_AS_ERROR target property were added to enable link with a linker-specific flag to treat warnings as errors.

• The cmake(1) command line gained the --link-no-warning-as-error option which causes the effects of the LINK_WARNING_AS_ERROR target property and CMAKE_LINK_WARNING_AS_ERROR variable to be ignored.