Replace local MUSL define with global ANDROID_HOST_MUSL

Bug: 190084016
Test: m USE_HOST_MUSL=true bionic-unit-tests-glibc
Change-Id: I56b23576cb24912112d2ae56d8ecc2e3716982fe
diff --git a/tests/netdb_test.cpp b/tests/netdb_test.cpp
index 381ba50..1cb569c 100644
--- a/tests/netdb_test.cpp
+++ b/tests/netdb_test.cpp
@@ -21,6 +21,7 @@
 #include <arpa/inet.h>
 #include <netinet/in.h>
 #include <string.h>
+#include <sys/cdefs.h>
 #include <sys/socket.h>
 #include <sys/types.h>
 
@@ -265,7 +266,7 @@
   ASSERT_EQ(0, hp->h_addr[0]);
 }
 
-#if defined(MUSL)
+#if defined(ANDROID_HOST_MUSL)
 // musl doesn't define NETDB_INTERNAL.  It also never sets *err to -1, but
 // since gethostbyname_r is a glibc extension, the difference in behavior
 // between musl and  glibc should probably be considered a bug in musl.