[libc++] Update a bad documentation link

EricWF · EricWF · commit d6fb02b196da · 2020-03-24T21:34:07.000-04:00
diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
@@ -1,4 +1,5 @@
-# See www/CMake.html for instructions on how to build libcxx with CMake.
+# See https://libcxx.llvm.org/docs/BuildingLibcxx.html for instructions on how
+# to build libcxx with CMake.
 
 #===============================================================================
 # Setup Project
