[macos] libpng build failures with Xcode13.3

/Volumes/Elephant/Users/jlaskey/Git/jdk/open/src/java.desktop/share/native/libsplashscreen/libpng/pngrutil.c:3584:20: error: performing pointer subtraction with a null pointer has undefined behavior [-Werror,-Wnull-pointer-subtraction]
                   png_isaligned(dp, png_uint_16) &&
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Volumes/Elephant/Users/jlaskey/Git/jdk/open/src/java.desktop/share/native/libsplashscreen/libpng/pngpriv.h:634:29: note: expanded from macro 'png_isaligned'
   (((type)((const char*)ptr-(const char*)0) & \
                            ^~~~~~~~~~~~~~~
/Volumes/Elephant/Users/jlaskey/Git/jdk/open/src/java.desktop/share/native/libsplashscreen/libpng/pngrutil.c:3585:20: error: performing pointer subtraction with a null pointer has undefined behavior [-Werror,-Wnull-pointer-subtraction]
                   png_isaligned(sp, png_uint_16) &&
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Volumes/Elephant/Users/jlaskey/Git/jdk/open/src/java.desktop/share/native/libsplashscreen/libpng/pngpriv.h:634:29: note: expanded from macro 'png_isaligned'
   (((type)((const char*)ptr-(const char*)0) & \
                            ^~~~~~~~~~~~~~~
/Volumes/Elephant/Users/jlaskey/Git/jdk/open/src/java.desktop/share/native/libsplashscreen/libpng/pngrutil.c:3592:23: error: performing pointer subtraction with a null pointer has undefined behavior [-Werror,-Wnull-pointer-subtraction]
                  if (png_isaligned(dp, png_uint_32) &&
                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Volumes/Elephant/Users/jlaskey/Git/jdk/open/src/java.desktop/share/native/libsplashscreen/libpng/pngpriv.h:634:29: note: expanded from macro 'png_isaligned'
   (((type)((const char*)ptr-(const char*)0) & \
                            ^~~~~~~~~~~~~~~
/Volumes/Elephant/Users/jlaskey/Git/jdk/open/src/java.desktop/share/native/libsplashscreen/libpng/pngrutil.c:3593:23: error: performing pointer subtraction with a null pointer has undefined behavior [-Werror,-Wnull-pointer-subtraction]
                      png_isaligned(sp, png_uint_32) &&
                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Volumes/Elephant/Users/jlaskey/Git/jdk/open/src/java.desktop/share/native/libsplashscreen/libpng/pngpriv.h:634:29: note: expanded from macro 'png_isaligned'
   (((type)((const char*)ptr-(const char*)0) & \
                            ^~~~~~~~~~~~~~~
/Volumes/Elephant/Users/jlaskey/Git/jdk/open/src/java.desktop/share/native/libsplashscreen/libpng/pngrutil.c:4652:34: error: performing pointer subtraction with a null pointer has undefined behavior [-Werror,-Wnull-pointer-subtraction]
         int extra = (int)((temp - (png_bytep)0) & 0x0f);
                                 ^ ~~~~~~~~~~~~
/Volumes/Elephant/Users/jlaskey/Git/jdk/open/src/java.desktop/share/native/libsplashscreen/libpng/pngrutil.c:4656:30: error: performing pointer subtraction with a null pointer has undefined behavior [-Werror,-Wnull-pointer-subtraction]
         extra = (int)((temp - (png_bytep)0) & 0x0f);
                             ^ ~~~~~~~~~~~~