Why does the shell I invoke Make with have an effect on its output?

[Peter0x44]

Hi all,

I have the following Makefile:

SHELLTYPE := posix
ifeq (.exe, $(findstring .exe,$(ComSpec)))
        SHELLTYPE := msdos
endif

default:
        $(info SHELLTYPE is $(SHELLTYPE))
        del

I am running it under Windows, using GNU Make 4.2

Note that in all cases, I have the executable `sh.exe` present in the PATH.
It is busybox-w32, renamed to sh.exe.
https://frippery.org/busybox

`del` is only present in the Makefile because it is a cmd.exe builtin command,
so if the build rules are being executed using cmd.exe, it should show "The
syntax of the command is incorrect.", while if it is a UNIX shell, it should
show an error relating to CreateProcess failing.

If I invoke this Makefile from cmd.exe, I get this output:

SHELLTYPE is msdos
del
process_begin: CreateProcess(NULL, del, ...) failed.
make (e=2): The system cannot find the file specified.
make: *** [Makefile:8: default] Error 2

If I invoke it from sh.exe, I get this different output:
make
SHELLTYPE is posix
del
process_begin: CreateProcess(NULL, del, ...) failed.
make (e=2): The system cannot find the file specified.
make: *** [Makefile:8: default] Error 2

Does anyone know why does the shell I invoke the Makefile with determines
whether it outputs "msdos" or "posix"? The built rules for both are *not* being
executed using cmd.exe, as you can tell by the error when trying to invoke
`del`, and the build rules of both Makefiles are being executed with the same
shell.

Lastly, I tried with msys2, and its bash shell:

HELLTYPE is posix
del
make: del: No such file or directory
make: *** [Makefile:9: default] Error 127

Best wishes,
Peter D.