xcur2png: fix cross-build

Fixes errors caused by autoconf not finding rpl_malloc

/nix/store/vl7wj0kj6rq3lgn7czb266lbr5y26kfn-aarch64-unknown-linux-gnu-binutils-2.42/bin/aarch64-unknown-linux-gnu-ld: /build/source/xcur2png.c:230:(.text+0x91c): undefined reference to `rpl_malloc'

pkgs/tools/graphics/xcur2png/default.nix

@@ -11,6 +11,11 @@ stdenv.mkDerivation rec {
     sha256 = "0858wn2p14bxpv9lvaz2bz1rk6zk0g8zgxf8iy595m8fqv4q2fya";
   };
 
+  patches = [
+    # https://github.com/eworm-de/xcur2png/pull/3
+    ./malloc.diff
+  ];
+
   nativeBuildInputs = [
     pkg-config
   ];

pkgs/tools/graphics/xcur2png/malloc.diff

@@ -0,0 +1,33 @@
+--- a/xcur2png.c
++++ b/xcur2png.c
+@@ -16,7 +16,10 @@
+ /* Todo: atoi error handling */
+ /* help is -h in manual */
+
++#if HAVE_CONFIG_H
+ #include <config.h>
++#endif
++#undef malloc
+
+ #define _ATFILE_SOURCE
+ #include <stdio.h>
+@@ -34,6 +37,19 @@
+ #include <png.h>
+ #include <X11/Xcursor/Xcursor.h>
+
++
++void *malloc ();
++
++/* Allocate an N-byte block of memory from the heap.
++   If N is zero, allocate a 1-byte block.  */
++
++void* rpl_malloc (size_t n)
++{
++  if (n == 0)
++    n = 1;
++  return malloc (n);
++}
++
+ #define PNG_SETJMP_NOT_SUPPORTED 1
+ 
+ #define PROGRESS_SHARPS 50 /* total number of progress sharps */