coverity/13765,13766,13767,13768: Fix memory leaks in hardcopy.c

The function mch_print_begin() returns early in case of an
error, but without freeing allocated memory.
To fix this, use stack allocation instead of heap allocation
for the variables res_prolog, res_encoding, res_cidfont and
res_cmap.
Travis: Remove Coverity build.

Coverity is now handled by neovim/bot-ci.
Use cmake --build instead of Make

- If possble try to abstract away from Make, and use cmake --build
- third-party still needs to find Make to build some components
- Removed search for Make from CMakeLists.txt
* for CMake < 3.0 --build has no color output
Removing code duplication in vim_strchr()

Logic defined in vim_strbyte() is duplicated at the end of vim_strchr().
Replacing duplicated code with a call to vim_strbyte().
nonnull arg function attribute on vim_strchr()
nonnull arg function attribute on vim_strbyte()