Lowercase windows imports

While windows and macOS are currently on case-insensitive file
systems, this poses no issue on those.  When cross compiling from
linux with a case sensitive file system and mingw providing only
lowercase headers, this in fact produces an issue.  As such we just
lowercase the import headers, which should still work fine on a
case insensitive file system and also enable mingw's headers to
be usable porperly.

driver/utils/dynwrapper.c

@@ -9,8 +9,8 @@ int rtsOpts;
 
 #include <stdarg.h>
 #include <stdio.h>
-#include <Windows.h>
-#include <Shlwapi.h>
+#include <windows.h>
+#include <shlwapi.h>
 
 #include "Rts.h"
 

rules/build-prog.mk

@@ -230,7 +230,7 @@ endif
 
 $1/$2/build/tmp/$$($1_$2_PROG)-inplace-wrapper.c: driver/utils/dynwrapper.c | $$$$(dir $$$$@)/.
 	$$(call removeFiles,$$@)
-	echo '#include <Windows.h>' >> $$@
+	echo '#include <windows.h>' >> $$@
 	echo '#include "Rts.h"' >> $$@
 	echo 'LPTSTR path_dirs[] = {' >> $$@
 	$$(foreach d,$$($1_$2_DEP_LIB_REL_DIRS),$$(call make-command,echo '    TEXT("/../../$$d")$$(comma)' >> $$@))
@@ -243,7 +243,7 @@ $1/$2/build/tmp/$$($1_$2_PROG)-inplace-wrapper.c: driver/utils/dynwrapper.c | $$
 
 $1/$2/build/tmp/$$($1_$2_PROG)-wrapper.c: driver/utils/dynwrapper.c | $$$$(dir $$$$@)/.
 	$$(call removeFiles,$$@)
-	echo '#include <Windows.h>' >> $$@
+	echo '#include <windows.h>' >> $$@
 	echo '#include "Rts.h"' >> $$@
 	echo 'LPTSTR path_dirs[] = {' >> $$@
 	$$(foreach p,$$($1_$2_TRANSITIVE_DEP_COMPONENT_IDS),$$(call make-command,echo '    TEXT("/../lib/$$p")$$(comma)' >> $$@))