Move selection of C++ STL into the build system.

Preparing for migration from stlport to libc++. STL selection is done
with LOCAL_CXX_STL (valid values are default, none, libc++,
libc++_static, stlport, stlport_static, bionic).

The selection of the STL is as follows:

    if LOCAL_CXX_STL == 'default'
      ifdef LOCAL_SDK_VERSION
        Use whatever STL the other NDK options have selected.
      else
        Use bionic's libstdc++ for target, GNU libstdc++ for host. This
        is compatible with the existing build options.
      endif
    else
      if LOCAL_CXX_STL == 'stlport'
        Use stlport.
      else if LOCAL_CXX_STL == 'libc++'
        Use libc++.
      else if LOCAL_CXX_STL == ''
        Don't use any STL.
      endif
    endif

Bug: 15193147
Change-Id: If712ba0ae7908d8147a69e29da5c453a183d6540
diff --git a/core/target_test_internal.mk b/core/target_test_internal.mk
index 95d4159..6b147b1 100644
--- a/core/target_test_internal.mk
+++ b/core/target_test_internal.mk
@@ -5,7 +5,17 @@
 LOCAL_CFLAGS += -DGTEST_OS_LINUX_ANDROID -DGTEST_HAS_STD_STRING
 
 LOCAL_C_INCLUDES += external/gtest/include
-ifneq ($(filter libc++,$(LOCAL_SHARED_LIBRARIES)),)
+
+my_test_libcxx := false
+ifndef LOCAL_SDK_VERSION
+ifeq (,$(TARGET_BUILD_APPS))
+ifeq ($(strip $(LOCAL_CXX_STL)),libc++)
+my_test_libcxx := true
+endif
+endif
+endif
+
+ifeq ($(my_test_libcxx),true)
 LOCAL_STATIC_LIBRARIES += libgtest_libc++ libgtest_main_libc++
 else
 LOCAL_STATIC_LIBRARIES += libgtest libgtest_main