Use capital letters for stdlib modules

Now use stdlib__String instead of stdlib__string. Removes a difference
between the stdlib when compiled with Dune vs make.

Changes

@@ -64,6 +64,13 @@ Working version
 - #9582: Add Array.{find_opt,find_map,split,combine}.
   (Nicolás Ojeda Bär, review by Daniel Bünzli and Gabriel Scherer)
 
+* #10169: Use capitalized module names in the Standard Library prefixing scheme
+  to match Dune, e.g. Stdlib__String instead of Stdlib__string. This is a
+  breaking change only to code which attempted to use the internal names before.
+  The Standard Library generated by the Dune rules is now equivalent to the main
+  build (the Dune rules still do not generate a distributable compiler).
+  (David Allsopp and Mark Shinwell, review by Gabriel Scherer)
+
 ### Other libraries:
 
 * #10084: Unix.open_process_args* functions now look up the program in the PATH.

Makefile

@@ -69,6 +69,8 @@ TOPLEVELSTART=toplevel/topstart.cmo
 
 TOPLEVELINIT=toplevel/toploop.cmo
 
+# This list is passed to expunge, which accepts both uncapitalized and
+# capitalized module names.
 PERVASIVES=$(STDLIB_MODULES) outcometree topdirs toploop
 
 LIBFILES=stdlib.cma std_exit.cmo *.cmi camlheader