Makefile: Make `git` check portable (POSIX compatible)

On systems using not the *GNU Bourne-Again SHell* (bash) as shell, the
git check might fail. This happens on Debian systems where the *Debian
Almquist Shell* (dash) is used by default for `/bin/sh`.

As a result, after running `make` the file `version.c` always contains
`unknown` instead of the correct version.

The problem is, that `type -p git` is not portable. Use `command -v`
instead [1][2].

> Where bash is your shell/hashbang, consistently use hash (for
> commands) or type (to consider built-ins & keywords).
>
> When writing a POSIX script, use command -v.

Fixes: #42

[1] https://stackoverflow.com/questions/592620/check-if-a-program-exists-from-a-bash-script
    "Check if a program exists from a Bash script"
[2] https://unix.stackexchange.com/questions/85249/why-not-use-which-what-to-use-then
    "Why not use “which”? What to use then?"

1 files changed, 1 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index 9dbbdbf..e4341fc 100644
--- a/Makefile
+++ b/Makefile
@@ -82,7 +82,7 @@ depend: .depend
 
 version.tmp: FORCE
 	( echo -n "char version[] = \"" ; 	\
-	if type -p git >/dev/null; then 	\
+	if command -v git >/dev/null; then 	\
 	if [ -d .git ] ; then 			\
 		git describe --tags HEAD | tr -d '\n'; 	\
 	else 					\