echo builtin doesn't handle end-of-options flag

[Todd A. Jacobs]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: darwin19.5.0
Compiler: clang
Compilation CFLAGS: -DSSH_SOURCE_BASHRC -Wno-parentheses -Wno-format-security
uname output: Darwin titan.local 19.6.0 Darwin Kernel Version 19.6.0: Thu Jun 
18 20:49:00 PDT 2020; root:xnu-6153.141.1~1/RELEASE_X86_64 x86_64
Machine Type: x86_64-apple-darwin19.5.0

Bash Version: 5.0
Patch Level: 18
Release Status: release

Description:
        The echo builtin accepts options, but does not seem to handle
        `--` correctly as the end of options. The expected behavior
        would be for -- to be removed, and any following flag-like
        substrings printed as-is.

Repeat-By:
        echo "-n"         # "" but expecting "-n"
        echo -- -n foo    # -- -n foo
        echo -- "-n foo"  # -- -n foo