COMP: Build curl as a static library

Following commit r22724 introducing the library "curl" (in place of "cmcurl"),
the library was build as shared.

This commit change the build of curl to be static to match how cmcurl
was also built.

Supporting a shared build would imply tweak to the launcher settings.

See 0001739

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22732 3bd1e089-480b-0410-8dfb-8563597acbee