When working on a C or C++ projects, it is often handy to compile a
single file (e.g. large refactoring where many files fail to compile so
compiling a single file results in less compiler errors making the compiler
output significantly easier to read and navigate). Current completion offers
only ninja targets which are usually just top level binaries. This commit makes
object files and library files to be offered in the ninja completion.
The change is inspired by the zsh ninja completion [1], but aims to reduce noise
by only matching for entries ending in ".o", ".so" or ".a".
[1] c828f06e08/src/zsh/_ninja (L30)
