readelf: Fix regression with multiple files and implicit debug_info reading.

readelf: Fix regression with multiple files and implicit debug_info reading.

Commit 314e9d7d "readelf: Handle .debug_info first if any other debug
section needs it" introduced a regression when handling multiple files.
The implicit and explicit printing of debuginfo weren't reset and so
the second file would not show (or scan) the .debug_info section when
needed.

Fix by resetting the implicit and explicit section printing flags.
Add a testcase that prints the .debug_loc section for two files and
check that the CUs are resolved.

Signed-off-by: Mark Wielaard <mark@klomp.org>