emulator/opengl: Fix Windows cross-build.

When building the host version of the gtest library, always
include -lpthread as part of LOCAL_LDLIBS, otherwise the build
will fail when cross-compiling for Windows on Linux.

Change-Id: I8614f9e6d543dbba910b9495d6c1bd59e7c61004

emulator/opengl/googletest.mk

@@ -45,6 +45,6 @@ LOCAL_CFLAGS += $(common_CFLAGS)
 LOCAL_C_INCLUDES += $(LOCAL_PATH)/include
 LOCAL_CPP_EXTENSION := .cc
 $(call emugl-export,C_INCLUDES,$(LOCAL_PATH)/include)
-$(call emugl-export,LDLIBS,$(common_LDLIBS))
+$(call emugl-export,LDLIBS,$(common_LDLIBS) -lpthread)
 LOCAL_HOST_BUILD := true
 $(call emugl-end-module)