Work around rmkdepend warning.

(cherry picked from commit 5756277ce59f3616d15662ef20d26424df2b591d)
Install custom assert.h in clang resource dir.

At least on Linux, the system assert.h has no include guards. This causes
re-parsing of it, even if it's included in a PCH. This in turn triggers
errors when running ROOT on a system with a different assert.h.

By adding a custom assert.h with include guards, the parsing is intercepted and
the assert.h as included in the PCH is taken. For the interpreter that's good
enough.

Still missing the CMake version.

(cherry picked from commit a08dd004d67dbfb7690a37db365875eff2e8b518)