Add comment ensuring include(GNUInstallDirs) stays where it should be.

pwnall · pwnall · commit f08cac9f7306 · 2019-11-04T00:22:23.000-08:00
diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -256,6 +256,7 @@ if(BUILD_SHARED_LIBS)
   set_property(TARGET crc32c_sse42 PROPERTY POSITION_INDEPENDENT_CODE TRUE)
 endif(BUILD_SHARED_LIBS)
 
+# Must be included before CMAKE_INSTALL_INCLUDEDIR is used.
 include(GNUInstallDirs)
 
 add_library(crc32c ""
