CMakeLists.txt: Move inclusion of `FindPkgConfig` down.

It must come after `CMAKE_TOOLCHAIN_FILE`.

Fixes #1167.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index cd04b97..d12897c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -121,7 +121,6 @@
 
 include(CheckIncludeFile)
 include(CMakeDependentOption)
-include(FindPkgConfig)
 
 # CMAKE_TOOLCHAIN_FILE must be set before `project' is called, which
 # configures the base build environment and references the toolchain file
@@ -245,6 +244,8 @@
 
 
 # Find dependencies
+include(FindPkgConfig)
+
 if (NOT FT_DISABLE_HARFBUZZ)
   set(HARFBUZZ_MIN_VERSION "2.0.0")
   if (FT_REQUIRE_HARFBUZZ)