Handle possible presence of library prefixes in MSVC.

- On MSVC, a Ceres dependency such as glog, may be named glog.lib, or
  libglog.lib.  By default, CMake assumes no prefix for libraries on
  MSVC when using find_library(), thus find_library(glog) would fail
  if glog was named libglog.lib.
- This patch caches & updates CMAKE_FIND_LIBRARY_PREFIXES in all of
  Ceres' find_package scripts to include lib & "" (no prefix) on MSVC
  and then returns CMAKE_FIND_LIBRARY_PREFIXES to its original state
  before returning.

Change-Id: Ic82799e3b786cfb7228a51183bc189578b072bbe