NMake Makefiles: Fix ICU builds

Fix the check conditions in config-msvc.mak and info-msvc.mak so that
the ICU items does indeed get built into the HarfBuzz main DLL, and that
the correct configuration info is displayed.

Also update the checks in detectenv-msvc.mak so that we can detect that
we are using Visual Studio 2017 (although the 2015-built binaries use
the same CRT DLL as the 2017 ones).

win32/info-msvc.mak

diff --git a/win32/info-msvc.mak b/win32/info-msvc.mak
index 9b92e03..70daf76 100644
--- a/win32/info-msvc.mak
+++ b/win32/info-msvc.mak
@@ -6,17 +6,21 @@
 
 !if "$(NO_UCDN)" != "1"
 UNICODE_IMPL = ucdn
-!else
-!if "$(GLIB)" == "1"
+!elseif "$(GLIB)" == "1"
 UNICODE_IMPL = GLib
+!elseif "$(ICU)" == "1"
+UNICODE_IMPL = ICU
+!endif
+
+!if "$(GLIB)" == "1"
 INC_FEATURES = $(INC_FEATURES) GLib
 BUILT_TOOLS = hb-shape.exe hb-ot-shape-closure.exe
 !if "$(CAIRO_FT)" == "1"
 BUILT_TOOLS = hb-view.exe $(BUILT_TOOLS)
 !endif
-!elseif "$(ICU)" == "1"
-UNICODE_IMPL = ICU
 !endif
+!if "$(ICU)" == "1"
+INC_FEATURES = $(INC_FEATURES) ICU
 !endif
 
 !if "$(FREETYPE)" == "1"