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

core/main.mk

@@ -390,6 +390,7 @@ subdirs := \
 	development/host \
 	development/tools/etc1tool \
 	development/tools/line_endings \
+	development/tools/emulator/opengl \
 	external/easymock \
 	external/expat \
 	external/libpng \

target/board/generic/BoardConfig.mk

@@ -36,3 +36,6 @@ TARGET_SHELL := mksh
 ifeq ($(HOST_OS),linux)
 WITH_DEXPREOPT := true
 endif
+
+# Build OpenGLES emulation guest and host libraries
+BUILD_EMULATOR_OPENGL := true

target/board/generic_x86/BoardConfig.mk

@@ -26,3 +26,6 @@ TARGET_SHELL := mksh
 ifeq ($(HOST_OS),linux)
 WITH_DEXPREOPT := true
 endif
+
+# Build OpenGLES emulation host and guest libraries
+BUILD_EMULATOR_OPENGL := true