emacs24: Add #define for building on Yosemite (darwin)

pkgs/applications/editors/emacs-24/at-fdcwd.patch

@@ -0,0 +1,13 @@
+diff --git a/lib/careadlinkat.h b/lib/careadlinkat.h
+index 5cdb813..7a272e8 100644
+--- a/lib/careadlinkat.h
++++ b/lib/careadlinkat.h
+@@ -23,6 +23,8 @@
+ #include <fcntl.h>
+ #include <unistd.h>
+ 
++#define AT_FDCWD -2
++
+ struct allocator;
+ 
+ /* Assuming the current directory is FD, get the symbolic link value

pkgs/applications/editors/emacs-24/default.nix

@@ -18,7 +18,10 @@ stdenv.mkDerivation rec {
     sha256 = "1zflm6ac34s6v166p58ilxrxbxjm0q2wfc25f8y0mjml1lbr3qs7";
   };
 
-  patches = [ ./darwin-new-sections.patch ];
+  patches = stdenv.lib.optionals stdenv.isDarwin [
+    ./darwin-new-sections.patch
+    ./at-fdcwd.patch
+  ];
 
   buildInputs =
     [ ncurses gconf libxml2 gnutls alsaLib pkgconfig texinfo ]