Enable more warnings in QMake-generated makefiles.

Use same warning levels for GCC than in original makefile. Use W4 level for Visual Studio.

src/src.pro

@@ -57,5 +57,17 @@ win32 {
     CONFIG += embed_manifest_exe console
     RC_FILE = cppcheck.rc
     HEADERS += resource.h
-	LIBS += -lshlwapi
+    LIBS += -lshlwapi
+}
+
+# Add more strict compiling flags for GCC
+# These flags are used in original (not generated by QMake) makefiles
+contains(QMAKE_CXX, g++) {
+    QMAKE_CXXFLAGS_WARN_ON += -Wextra -pedantic
+}
+
+# Change Visual Studio compiler (CL) warning level to W4
+contains(QMAKE_CXX, cl) {
+    QMAKE_CXXFLAGS_WARN_ON -= -W3
+    QMAKE_CXXFLAGS_WARN_ON += -W4
 }