Get new/delete from libc++.

This is what we do in the platform, and libc++abi isn't properly
configured to provide definitions for aligned new/delete.

Test: ndk/checkbuild.py && ndk/run_tests.py
Bug: https://github.com/android-ndk/ndk/issues/869
Change-Id: I92e54d1cd0f1605e3eb8e4698ab064a5be28116c
(cherry picked from commit 044186190ed5a6a2f7a25c5fff971201135f5946)
diff --git a/Android.mk b/Android.mk
index 06d2d87..b2b9615 100644
--- a/Android.mk
+++ b/Android.mk
@@ -67,7 +67,6 @@
     -std=c++1z \
     -DLIBCXX_BUILDING_LIBCXXABI \
     -D_LIBCPP_BUILDING_LIBRARY \
-    -D_LIBCPP_DISABLE_NEW_DELETE_DEFINITIONS \
     -D__STDC_FORMAT_MACROS \
     $(libcxx_export_cxxflags) \