Fix some build symbol configuration.
Remove -gdwarf-4 from GYP build. This is the default for GCC 4.8 which is now required, so this command-line argument is redundant.
Only set use_debug_fission in the GN build in debug mode. This matches GYP. Release mode symbols will be non-fission.
Implement linux_symbols target in GN. Convert dump_app_syms from sh to Python for better GN usability, and it's more readable for normal programmers on the team.
BUG=
Review URL: https://codereview.chromium.org/
1179393004
Cr-Commit-Position: refs/heads/master@{#334510}