[aat] Try fixing VC bots

c:\projects\harfbuzz\src\hb-aat-layout-common-private.hh(51): error C2872: 'UINT16': ambiguous symbol [C:\projects\harfbuzz\build\harfbuzz.vcxproj]
C:\Program Files (x86)\Windows Kits\10\Include\10.0.14393.0\shared\basetsd.h(80): note: could be 'unsigned short UINT16'
c:\projects\harfbuzz\src\hb-open-type-private.hh(648): note: or       'OT::UINT16'
diff --git a/src/hb-aat-layout-common-private.hh b/src/hb-aat-layout-common-private.hh
index 47efb49..1c6a4af 100644
--- a/src/hb-aat-layout-common-private.hh
+++ b/src/hb-aat-layout-common-private.hh
@@ -33,6 +33,9 @@
 namespace AAT {
 
 using namespace OT;
+using OT::UINT8;
+using OT::UINT16;
+using OT::UINT32;
 
 
 /*
diff --git a/src/hb-aat-layout-morx-table.hh b/src/hb-aat-layout-morx-table.hh
index c59616e..db4a498 100644
--- a/src/hb-aat-layout-morx-table.hh
+++ b/src/hb-aat-layout-morx-table.hh
@@ -37,6 +37,9 @@
 namespace AAT {
 
 using namespace OT;
+using OT::UINT8;
+using OT::UINT16;
+using OT::UINT32;
 
 
 struct RearrangementSubtable