Remove spurious "-C" flag from CMake command lines in build.html.

-C usually specifies a script to prepopulate the CMake cache. In this case no
script is specified, so CMake appears to just ignore it. So don't mention it
in the first place - it's not desired anyways.

Reviewed by: Daniel Malea



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@186964 91177308-0d34-0410-b5e6-96231b3b80d8