t7810: improve check of -W with user-defined function lines
The check for function context (-W) together with user-defined function
line patterns reuses hello.c and pretends it's written in a language in
which function lines contain either "printf" or a trailing curly brace.
That's a bit obscure.
Make the test easier to read by adding a small PowerShell script, using
a simple, but meaningful expression, and separating out checks for
different aspects into dedicated tests instead of simply matching the
whole output byte for byte.
Also include a test for showing comments before function lines like git
Signed-off-by: Junio C Hamano <gitster@pobox.com>