install: Make ATL headers use consistent lower case includes of other…

… headers

This makes clang-cl use of e.g. atlbase.h work on case sensitive file
systems (as atlbase.h originally includes OleCtl.h), and makes MSVC use
of atlbase.h produce dependency files that don't require files to be
rebuilt every time.

This should fix #167.

install.sh

@@ -73,6 +73,11 @@ cd ..
 # and the call to fixinclude lowercases those references.
 "$ORIG"/lowercase -symlink include
 "$ORIG"/fixinclude include
+if [ -d "atlmfc/include" ]; then
+    # The ATL headers are lowercased themselves, but they refer to
+    # WinSDK headers with mixed casing.
+    "$ORIG"/fixinclude "atlmfc/include"
+fi
 cd bin
 # vctip.exe is known to cause problems at some times; just remove it.
 # See https://bugs.chromium.org/p/chromium/issues/detail?id=735226 and