Fix path in BUILD.gn file.

Unbreaks the build when pdf_enable_xfa=true.

BUG=
R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1898313002
diff --git a/BUILD.gn b/BUILD.gn
index 74ffa17..026ffc5 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -641,9 +641,9 @@
   ]
   if (pdf_enable_xfa) {
     sources += [
+      "core/fxcrt/fx_arabic.cpp",
       "core/fxcrt/fx_arabic.h",
       "core/fxcrt/fx_basic_maps.cpp",
-      "core/fxcrt/include/fx_arabic.cpp",
       "core/fxcrt/include/fx_arb.h",
     ]
   }