gcc: Disabled most warnings

There are hundreds of warnings from the old C code, such as
signed/unsigned comparisons and comparisons that are always true
due to value range. These are now disabled as it is unlikely
that all of these will be fixed for the legacy code.

TODO: Enable strict warnings for new C++ code.

doomsday/config.pri

@@ -78,12 +78,9 @@ unix {
     # Unix/Mac build options.
     DEFINES += UNIX
 
-    # We are not interested in unused parameters (there are quite a few).
-    QMAKE_CFLAGS_WARN_ON += \
-        -Wno-unused-parameter \
-        -Wno-unused-variable \
-        -Wno-missing-field-initializers \
-        -Wno-missing-braces
+    # Ease up on the warnings. (The old C code is a bit messy.)
+    QMAKE_CFLAGS_WARN_ON -= -Wall
+    QMAKE_CFLAGS_WARN_ON -= -W
 }
 unix:!macx {
     # Generic Unix build options.