Cherry-pick local changes to 9.2

Cherry-picked commits:
    b711aa82: Add Unix domain socket support to gdbserver 7.9.1.
    4c58332d: Go back to snprintf rather than strlcpy.
    c64829b2: Fallback to open if multifs_open fails.
    21770732: Fix gdbserver process interruption.
    35ee6839: Remove gdb hack.
    78af0f6f: Handle cross compile for locale configuration
    dfc5ca4a: Set the default gdb osabi to GNU/Linux.
    5cbd102d: Specify osabi in arm/aarch64 tdescs. (updated)
    d378e661: Explicit link -ldl for gdbserver

Test: build
Change-Id: Iea7f0159ad5d4f5edba0db215a96bc85b3f332cd