Make the HWCAP/HWCAP2 constants available from <sys/auxv.h>.

Noticed by ARM when adding BTI support to the linker.

Test: treehugger
Change-Id: If3b87d0bd4682ff478b7805251fc9a88a7f439f9
diff --git a/tests/Android.bp b/tests/Android.bp
index 4bd96ad..d1afd51 100644
--- a/tests/Android.bp
+++ b/tests/Android.bp
@@ -166,6 +166,7 @@
         "strings_nofortify_test.cpp",
         "strings_test.cpp",
         "sstream_test.cpp",
+        "sys_auxv_test.cpp",
         "sys_epoll_test.cpp",
         "sys_mman_test.cpp",
         "sys_msg_test.cpp",