gdb-add-index: accept a list of files to index
gdb-add-index: accept a list of files to index

Previously gdb-add-index took a single binary argument to index. It uses
ldd to get its dependencies and index those too. Now it accepts more than
one file, along with a -n option to not attempt to extract dependencies.
This is useful for Android development where there's no single
binary to index. Now you can do gdb-add-index -n out/Debug/lib.unstripped/*

This CL also cleans up the style a bit for consistency.

BUG=

Review URL: https://codereview.chromium.org/1471523002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#361227}

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