COMP: External_curl - Properly set curl_DIR on multi-config system

The output directory is expected to be:

   <CURL_DIR>/lib/{Release, Debug, ..}

and not

   <CURL_DIR>/{Release, Debug, ..}/lib

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22731 3bd1e089-480b-0410-8dfb-8563597acbee
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 #1739

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