Use env as interpreter for all exe and scripts.

Git requires a MSYS2 perl. However, there are many distributions
of perl. If another perl is in the PATH in front of the MSYS2 one,
git will mistakenly find it. The shebang is right #!/usr/bin/perl,
but actually git only recognizes perl and finds the first one in
the PATH.

This pull request removes the naïve parser of shebang, and just finds
`env.exe` as the interpreter. It should be in the `PATH` in MSYS2.

Signed-off-by: Yuyi Wang <Strawberry_Str@hotmail.com>

compat/mingw.c

@@ -1530,41 +1530,6 @@ static const char *quote_arg_msys2(const char *arg)
 	return strbuf_detach(&buf, 0);
 }
 
-static const char *parse_interpreter(const char *cmd)
-{
-	static char buf[MAX_PATH];
-	char *p, *opt;
-	int n, fd;
-
-	/* don't even try a .exe */
-	n = strlen(cmd);
-	if (n >= 4 && !strcasecmp(cmd+n-4, ".exe"))
-		return NULL;
-
-	fd = open(cmd, O_RDONLY);
-	if (fd < 0)
-		return NULL;
-	n = read(fd, buf, sizeof(buf)-1);
-	close(fd);
-	if (n < 4)	/* at least '#!/x' and not error */
-		return NULL;
-
-	if (buf[0] != '#' || buf[1] != '!')
-		return NULL;
-	buf[n] = '\0';
-	p = buf + strcspn(buf, "\r\n");
-	if (!*p)
-		return NULL;
-
-	*p = '\0';
-	if (!(p = strrchr(buf+2, '/')) && !(p = strrchr(buf+2, '\\')))
-		return NULL;
-	/* strip options */
-	if ((opt = strchr(p+1, ' ')))
-		*opt = '\0';
-	return p+1;
-}
-
 /*
  * exe_only means that we only want to detect .exe files, but not scripts
  * (which do not have an extension)
@@ -2151,39 +2116,31 @@ pid_t mingw_spawnvpe(const char *cmd, const char **argv, char **deltaenv,
 		pid = -1;
 	}
 	else {
-		const char *interpr = parse_interpreter(prog);
-
-		if (interpr) {
-			const char *argv0 = argv[0];
-			char *iprog = path_lookup(interpr, 1);
+		const char *interpr = "env.exe";
+		const char *argv0 = argv[0];
+		char *iprog = path_lookup(interpr, 1);
+		if (!iprog) {
+			errno = ENOENT;
+			pid = -1;
+		}
+		else {
 			argv[0] = prog;
-			if (!iprog) {
-				errno = ENOENT;
-				pid = -1;
-			}
-			else {
-				pid = mingw_spawnve_fd(iprog, argv, deltaenv, dir, interpr,
-						       fhin, fhout, fherr);
-				free(iprog);
-			}
+			pid = mingw_spawnve_fd(iprog, argv, deltaenv, dir, interpr,
+							fhin, fhout, fherr);
+			free(iprog);
 			argv[0] = argv0;
 		}
-		else
-			pid = mingw_spawnve_fd(prog, argv, deltaenv, dir, NULL,
-					       fhin, fhout, fherr);
 		free(prog);
 	}
 	return pid;
 }
 
 static int try_shell_exec(const char *cmd, char *const *argv)
 {
-	const char *interpr = parse_interpreter(cmd);
+	const char *interpr = "env.exe";
 	char *prog;
 	int pid = 0;
 
-	if (!interpr)
-		return 0;
 	prog = path_lookup(interpr, 1);
 	if (prog) {
 		int exec_id;