riscv64: add <sys/hwprobe.h>.

This is source compatible with the current proposal for glibc.

Bug: https://github.com/google/android-riscv64/issues/27
Test: treehugger
Change-Id: I428777e4eac1fe643d442a93a4b3ad1fdf0ffd97
diff --git a/tests/Android.bp b/tests/Android.bp
index 8dc8eaf..a4298ab 100644
--- a/tests/Android.bp
+++ b/tests/Android.bp
@@ -472,6 +472,7 @@
         "sys_auxv_test.cpp",
         "sys_cachectl_test.cpp",
         "sys_epoll_test.cpp",
+        "sys_hwprobe_test.cpp",
         "sys_mman_test.cpp",
         "sys_msg_test.cpp",
         "sys_param_test.cpp",