Whether the full path to the MSYS2 Bash is specified using backslashes
or forward slashes, in either case the command-line arguments need to be
quoted in the MSYS2-specific manner instead of using regular Win32
command-line quoting rules.
In preparation for `prepare_shell_cmd()` to use the full path to
`sh.exe` (with forward slashes for consistency), let's teach the
`is_msys2_sh()` function about this; Otherwise 5580.4 'clone with
backslashed path' would fail once `prepare_shell_cmd()` uses the full
path instead of merely `sh`.
This patch relies on the just-introduced fix where `fspathcmp()` handles
backslashes and forward slashes as equivalent on Windows.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>