Ensure installed stdlib artefacts have correct case

Changes

@@ -114,11 +114,12 @@ Working version
 - #9582: Add Array.{find_opt,find_map,split,combine}.
   (Nicolás Ojeda Bär, review by Daniel Bünzli and Gabriel Scherer)
 
-* #10169, #10270: 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).
+* #10169, #10270, #10301: 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:

stdlib/Makefile

@@ -56,6 +56,10 @@ allopt: stdlib.cmxa std_exit.cmx
 opt.opt: allopt
 
 .PHONY: install
+# Ensure any pre-4.13 lowercased artefacts are removed on macOS and Windows
+install::
+	rm -f $(INSTALL_LIBDIR)/stdlib__*.cmi
+
 install::
 	$(INSTALL_DATA) \
 	  stdlib.cma std_exit.cmo *.cmi camlheader_ur \
@@ -81,7 +85,11 @@ endif
 installopt: installopt-default
 
 .PHONY: installopt-default
-installopt-default:
+# Ensure any pre-4.13 lowercased artefacts are removed on macOS and Windows
+installopt-default::
+	rm -f $(INSTALL_LIBDIR)/stdlib__*.cmx
+
+installopt-default::
 	$(INSTALL_DATA) \
 	  stdlib.cmxa stdlib.$(A) std_exit.$(O) *.cmx \
 	  "$(INSTALL_LIBDIR)"