MinGW: Quote arguments for subprocesses that contain a single-quote

Before a process can be spawned by mingw_spawnve, arguments must be
surrounded by double-quotes if special characters are present.  This is
necessary because the startup code of the spawned process will expand
arguments that look like glob patterns.  "Normal" Windows command line
utilities expand only * and ?, but MSYS programs, including bash, are
different: They also expand braces, and this has already been taken care
of by compat/mingw.c:quote_arg().

But MSYS programs also treat single-quotes in a special way: Arguments
between single-quotes are spliced together (with spaces) into a word.
With this patch this treatment is avoided by quoting arguments that contain
single-quotes.

This lets t4252 pass on Windows.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/mingw.c

@@ -457,7 +457,7 @@ static const char *quote_arg(const char *arg)
 	const char *p = arg;
 	if (!*p) force_quotes = 1;
 	while (*p) {
-		if (isspace(*p) || *p == '*' || *p == '?' || *p == '{')
+		if (isspace(*p) || *p == '*' || *p == '?' || *p == '{' || *p == '\'')
 			force_quotes = 1;
 		else if (*p == '"')
 			n++;