Makefile: add several shell targets

This adds several shell targets for the most used shells.

Note: The target runs dosh -c "$SHELL", i.e. it does not run the $SHELL
directly. As a consequence, dosh does not go in interactive mode and
does not allocate a pseudo-TTY as not interactive flag is explicitly set
and the shell command has arguments. Thus, the interactive $SHELL ends.
The targets appends explicitly the interactive option via the variable
.SHELLFLAGS[1].

[1]: https://www.gnu.org/software/make/manual/html_node/Choosing-the-Shell.html

Makefile

@@ -1,5 +1,5 @@
 #
-# Copyright 2017-2020,2023-2024 Gaël PORTAY
+# Copyright 2017-2020,2023-2025 Gaël PORTAY
 #
 # SPDX-License-Identifier: LGPL-2.1-or-later
 #
@@ -196,6 +196,13 @@ aur-git: PKGBUILD.tmp
 PKGBUILD.tmp: PKGBUILD-git
 	cp $< $@
 
+.PHONY: sh dash bash zsh
+sh dash bash zsh: PATH := $(CURDIR):$(PATH)
+sh dash bash zsh: .SHELLFLAGS := -c -i
+sh dash bash zsh: SHELL := dosh
+sh dash bash zsh:
+	$@
+
 %.1: %.1.adoc
 	asciidoctor -b manpage -o $@ $<