Fix:

fatal error: 'fp.h' file not found

https://github.com/pnggroup/libpng/commit/893b8113f04d408cc6177c6de19c9889a48faa24
--- pngpriv.h.orig	2017-08-29 16:01:23.000000000 -0500
+++ pngpriv.h	2025-02-05 09:56:47.000000000 -0600
@@ -508,18 +508,7 @@
     */
 #  include <float.h>
 
-#  if (defined(__MWERKS__) && defined(macintosh)) || defined(applec) || \
-    defined(THINK_C) || defined(__SC__) || defined(TARGET_OS_MAC)
-   /* 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