Fix:

fatal error: 'fp.h' file not found

https://github.com/pnggroup/libpng/commit/893b8113f04d408cc6177c6de19c9889a48faa24
--- libs/png/pngconf.h.orig	2012-06-06 06:59:01.000000000 -0500
+++ libs/png/pngconf.h	2025-02-05 10:02:40.000000000 -0600
@@ -382,17 +382,7 @@
  */
 
 #if defined(PNG_FLOATING_POINT_SUPPORTED)
-#  if defined(MACOS)
-     /* We need to check that <math.h> hasn't already been included earlier
-      * as it seems it doesn't agree with <fp.h>, yet we should really use
-      * <fp.h> if possible.
-      */
-#    if !defined(__MATH_H__) && !defined(__MATH_H) && !defined(__cmath__)
-#      include <fp.h>
-#    endif
-#  else
 #    include <math.h>
-#  endif
 #  if defined(_AMIGA) && defined(__SASC) && defined(_M68881)
      /* Amiga SAS/C: We must include builtin FPU functions when compiling using
       * MATH=68881