pgsql: Don't hard-code the input file name in gen_tabcomplete.pl's outp

Don't hard-code the input file name in gen_tabcomplete.pl's output.

Use $ARGV[0], that is the specified input file name, in #line
directives generated by gen_tabcomplete.pl. This makes code
coverage reports work properly in the meson build system (where
the input file name will be a relative path).

Also fix up brain fade in the meson build rule for tab-complete.c:
we only need to write the input file name once not twice.

Jacob Champion (some cosmetic adjustments by me)

Discussion: /messages/by-id/CAOYmi+=+oWAoi8pqnH0MJQqsSn4ddzqDhqRQJvyiN2aJSWvw2w@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/c75c6f8d280a3364643fc51f9c9fdf2dee0213c2

Modified Files
--------------
src/bin/psql/gen_tabcomplete.pl | 17 +++++++++--------
src/bin/psql/meson.build | 4 ++--
2 files changed, 11 insertions(+), 10 deletions(-)