gitignore: ignore object file temporaries

During a build, a lot of *.o.-hash files are created - had not noticed
this as they are usually dumped in tmpfs on Linux. However, they
sometimes are present during a long build in the project directory, making it
annoying to commit while the project is being built.

These have been observed with Clang, -fsanitize-undefined on Arch Linux,
though other configurations may also generate such temporaries.

The solution here is on lines with the Linux kernel's .gitignore:
https://github.com/torvalds/linux/blob/master/.gitignore.
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

.gitignore

 *.a
 *.o
+*.o.*
 *.d
 *.def
 *.dll