emulator: Enable GLES emulation libraries

This patch enables the build of OpenGLES emulation libraries
(both in the guest and the host) for any emulator-specific
product config.

+ update core/main.mk to ensure that the right path is parsed
  when building the Windows SDK

Change-Id: Ifde047f8c0ef922504a7286c8c5b57f7c79c71f8
diff --git a/core/main.mk b/core/main.mk
index b4282ee..7f37f0e 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -390,6 +390,7 @@
 	development/host \
 	development/tools/etc1tool \
 	development/tools/line_endings \
+	development/tools/emulator/opengl \
 	external/easymock \
 	external/expat \
 	external/libpng \