freetype: enable 64-bit API on 32-bit systems

Without the change `pkgsi686Linux.fontconfig` test fails to find the font
on filesystems with 64-bit inodes:

    fontconfig> FAIL: test-bz106632

This happens because `freetype` uses 32-bit `fstat()` API in
builds/unix/ftsystem.c without explicit 64-bit bit switch on.

pkgs/development/libraries/freetype/default.nix

@@ -55,7 +55,8 @@ stdenv.mkDerivation (finalAttrs: {
   CC_BUILD = "${buildPackages.stdenv.cc}/bin/cc";
 
   # The asm for armel is written with the 'asm' keyword.
-  CFLAGS = lib.optionalString stdenv.isAarch32 "-std=gnu99";
+  CFLAGS = lib.optionalString stdenv.isAarch32 "-std=gnu99"
+    + lib.optionalString stdenv.hostPlatform.is32bit " -D_FILE_OFFSET_BITS=64";
 
   enableParallelBuilding = true;