QMimeDatabase/xml: support both 'xmlstarlet' and 'xml' for minifying XML

Commit 370324f6e2 changed the call to 'xml' to 'xmlstarlet' because
some Linux distributions do not provide a binary called xml. Anyhow,
the official Windows packages of xmlstarlet only provide 'xml.exe'.

Therefore just check for both.

Pick-to: 5.15 6.0
Change-Id: I4381b256850e4101b760df21f2b0baffb4414620
Reviewed-by: Eric Lemanissier <eric.lemanissier@gmail.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/mimetypes/mime/generate.pl

@@ -71,6 +71,10 @@ if (checkCommand("xmlstarlet")) {
     # Minify the data before compressing
     $cmd = "xmlstarlet sel -D -B -t -c / $fname";
     $cmd .= "| $compress" if $compress;
+} elsif (checkCommand("xml")) {
+    # Minify the data before compressing
+    $cmd = "xml sel -D -B -t -c / $fname";
+    $cmd .= "| $compress" if $compress;
 } elsif ($compress) {
     $cmd = "$compress < $fname"
 }