CMakeLists.txt: Fix `Info.plist` path.

When building a framework using CMake with `add_subdirectory`, CMake must be
able to find `freetype-Info.plist` when configuring the framework
properties.

Fixes #1145.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8d6e16a..5e3345d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -491,7 +491,7 @@
   )
   set_target_properties(freetype PROPERTIES
     FRAMEWORK TRUE
-    MACOSX_FRAMEWORK_INFO_PLIST builds/mac/freetype-Info.plist
+    MACOSX_FRAMEWORK_INFO_PLIST ${CMAKE_CURRENT_SOURCE_DIR}/builds/mac/freetype-Info.plist
     PUBLIC_HEADER "${PUBLIC_HEADERS}"
     XCODE_ATTRIBUTE_INSTALL_PATH "@rpath"
   )