COMP: Fix 'ninja' build error specifying 'make' command to build OpenSSL.

Since OpenSSL build system doesn't provide ninja files, it is important
to explicitly specify that it should be built using ninja.

Error was the following:

[7/9] Performing build step for 'Slicer'
FAILED: cd /home/jchris/Projects/SarrpTPS-SuperBuild-Release-Qt485-N/Slicer-build && /home/jchris/Support/cmake-2.8.11.2/bin/cmake --build /home/jchris/Projects/SarrpTPS-SuperBuild-Release-Qt485-N/Slicer-build --config . && /home/jchris/Support/cmake-2.8.11.2/bin/cmake -E touch /home/jchris/Projects/SarrpTPS-SuperBuild-Release-Qt485-N/CMake/Superbuild/Slicer-cmake/src/Slicer-stamp/Slicer-build
ninja: error: build.ninja:726: bad $-escape (literal $ must be written as $$)

ninja: build stopped: subcommand failed.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22837 3bd1e089-480b-0410-8dfb-8563597acbee