Add compile time define that was missing.

There used to be a check for `__has_include(<cxxabi.h>)`, but it
was removed because it is a clang extension. This adds
-DLIBCXX_BUILDING_LIBCXXABI to the mk and bp files to fix this.

Change-Id: Ife2f93ace8c2766c0140fba88bf74a941ed8e57e
diff --git a/Android.bp b/Android.bp
index 41de673..bf9ee58 100644
--- a/Android.bp
+++ b/Android.bp
@@ -54,6 +54,7 @@
         "-std=c++14",
         "-nostdinc++",
         "-fexceptions",
+        "-DLIBCXX_BUILDING_LIBCXXABI",
     ],
     rtti: true,
     whole_static_libs: [
diff --git a/Android.mk b/Android.mk
index f032a6c..7e28736 100644
--- a/Android.mk
+++ b/Android.mk
@@ -52,6 +52,7 @@
     -std=c++14 \
     -nostdinc++ \
     -fexceptions \
+    -DLIBCXX_BUILDING_LIBCXXABI \
 
 # target static lib
 include $(CLEAR_VARS)