QMimeDatabase: allow building without our internal copy

Saves 234kB of read-only data (when compressed with zstd) in QtCore,
plus one load-time execution. With Zlib, the size was 315 kB.

[ChangeLog][QtCore][QMimeDatabase] Added configure option
-no-mimetype-database that tells Qt not to bundle its own copy of the
XDG MIME database. If this option is passed, QMimeDatabase will only
work if there's a system copy in $XDG_DATA_DIRS/mime. This option is
useful for Linux distributions that ensure the data is always present.

Change-Id: I1004b4b819774c4c9296fffd158e69c490e88fb6
Reviewed-by: David Faure <david.faure@kdab.com>

src/corelib/configure.json

@@ -11,6 +11,7 @@
             "icu": "boolean",
             "inotify": "boolean",
             "journald": "boolean",
+            "mimetype-database": "boolean",
             "pcre": { "type": "enum", "values": [ "qt", "system" ] },
             "posix-ipc": { "type": "boolean", "name": "ipc_posix" },
             "pps": { "type": "boolean", "name": "qqnx_pps" },
@@ -678,6 +679,11 @@
             "condition": "features.textcodec",
             "output": [ "publicFeature", "feature" ]
         },
+        "mimetype-database": {
+            "label": "Built-in copy of the MIME database",
+            "condition": "features.mimetype",
+            "output": [ "privateFeature" ]
+        },
         "system-pcre2": {
             "label": "Using system PCRE2",
             "disable": "input.pcre == 'qt'",
@@ -1048,6 +1054,7 @@ Please apply the patch corresponding to your Standard Library vendor, found in
                 "glib",
                 "iconv",
                 "icu",
+                "mimetype-database",
                 {
                     "message": "Tracing backend",
                     "type": "firstAvailableFeature",

src/corelib/mimetypes/mimetypes.pri

@@ -21,5 +21,5 @@ qtConfig(mimetype) {
         mimetypes/qmimeglobpattern.cpp \
         mimetypes/qmimeprovider.cpp
 
-    RESOURCES += mimetypes/mimetypes.qrc
+    qtConfig(mimetype-database): RESOURCES += mimetypes/mimetypes.qrc
 }

src/corelib/mimetypes/qmimeprovider.cpp

@@ -54,7 +54,9 @@
 
 static void initResources()
 {
+#if QT_CONFIG(mimetype_database)
     Q_INIT_RESOURCE(mimetypes);
+#endif
 }
 
 QT_BEGIN_NAMESPACE