pdflib: Fix build with recent clang

Closes: https://trac.macports.org/ticket/71998

print/pdflib/Portfile

@@ -24,6 +24,7 @@ patchfiles          patch-configure.diff \
                     implicit.patch \
                     arm64.patch \
                     patch-perl_Makefile.diff \
+                    patch-pngconf.h.diff \
                     patch-libtool.diff
 
 configure.ccache    no

print/pdflib/files/patch-pngconf.h.diff

@@ -0,0 +1,25 @@
+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