[CMake] Update cmake/modules/UseLATEX.cmake to version 1.10.4.

Whitespace changes where necessary to please the git commit hook.
[CMake] Apply our modifications to UseLATEX.cmake.

Needed to build the documentation only for make doc.
Avoid name clashes by adding MANGLE_TARGET_NAMES.
With CMake 3.0.0 no more warnings are emitted by
building the documentation.