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/netinet_in_test.cpp b/tests/netinet_in_test.cpp
index 8343f57..b7dd7c5 100644
--- a/tests/netinet_in_test.cpp
+++ b/tests/netinet_in_test.cpp
@@ -17,6 +17,7 @@
 #include <netinet/in.h>
 
 #include <errno.h>
+#include <sys/cdefs.h>
 
 #include <gtest/gtest.h>
 
@@ -31,7 +32,7 @@
 static constexpr uint64_t be64 = 0xf0debc9a78563412;
 
 TEST(netinet_in, bindresvport) {
-#if !defined(MUSL)
+#if !defined(ANDROID_HOST_MUSL)
   // This isn't something we can usually test (because you need to be root),
   // so just check the symbol's there.
   ASSERT_EQ(-1, bindresvport(-1, nullptr));