message: Add additional warnings used by NAS2D
  A few used by NAS2D were omitted since they trigger warnings:
  `-Wextra`
  `-Wpedantic`
  `-Wzero-as-null-pointer-constant`
  `-Wold-style-cast`
  `-Wdouble-promotion`
  `-Wmissing-declarations`
  `-Wswitch-enum`
  `-Wswitch-default`
  `-Wredundant-decls`
diff: @@ -10,7 +10,7 @@ NAS2DLIBDIR := $(NAS2DDIR)lib/
  NAS2DLIB := $(NAS2DLIBDIR)libnas2d.a
  CPPFLAGS := $(CPPFLAGS_EXTRA)
  -CXXFLAGS_WARN := -Wall -Wno-unknown-pragmas $(WARN_EXTRA)
  +CXXFLAGS_WARN := -Wall -Wno-unknown-pragmas -Wnull-dereference -Wcast-qual -Wcast-align -Wshadow -Wnon-virtual-dtor -Woverloaded-virtual -Wmissing-include-dirs -Winvalid-pch -Wmissing-format-attribute $(WARN_EXTRA)
  CXXFLAGS := $(CXXFLAGS_EXTRA) -std=c++17 $(CXXFLAGS_WARN) -I$(NAS2DINCLUDEDIR) $(shell sdl2-config --cflags)
  LDFLAGS := $(LDFLAGS_EXTRA) -L$(NAS2DLIBDIR) $(shell sdl2-config --libs)
  LDLIBS := $(LDLIBS_EXTRA) -lnas2d -lSDL2 -lSDL2_image -lSDL2_mixer -lSDL2_ttf -lphysfs -lGL -lGLEW
  