pngcrush: Fix build with recent clang

Closes: https://trac.macports.org/ticket/71631

graphics/pngcrush/Portfile

@@ -28,7 +28,8 @@ use_xz              yes
 checksums           rmd160  ff93938e8e6ba8565386efdb51962f16b138a27d \
                     sha256  8fc18bcbcc65146769241e20f9e21e443b0f4538d581250dce89b1e969a30705
 
-patchfiles          patch-Makefile.diff
+patchfiles          patch-Makefile.diff \
+                    patch-pngpriv.h.diff
 
 # cannot use SSE includes on snowleopard, #52419
 if {${os.platform} eq "darwin" && ${os.major} <= 10} {

graphics/pngcrush/files/patch-pngpriv.h.diff

@@ -0,0 +1,26 @@
+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