Only generate breakpad symbols for ELF binaries

When BREAKPAD_GENERATE_SYMBOLS is set to true, the build will attempt
to run dump_syms for all dynamic binaries.  However some build targets
are now using cc_prebuilt_binary for installing python host scripts.
This causes dump_syms to return an error, causing the build to fail.
So check instead if the file is an ELF binary before running dump_syms.

Bug: 65065674
Test: Built AT target successfully.
Change-Id: Ibe7d3ebd312376600cf21efa111489451a4e7578