Build bionic unit tests for musl

Modify bionic unit tests that are built for glibc so that they also
build against musl.  They don't all pass though:

With glibc:
 2 SLOW TESTS
 4 TIMEOUT TESTS
313 FAILED TESTS
  YOU HAVE 2 DISABLED TESTS

With musl:
11 SLOW TESTS
11 TIMEOUT TESTS
363 FAILED TESTS
  YOU HAVE 2 DISABLED TESTS

Bug: 190084016
Test: m bionic-unit-tests-glibc with musl
Test: atest bionic-unit-tests-static
Test: atest --host bionic-unit-tests-glibc with glibc
Change-Id: I79b6eab04fed3cc4392450df5eef2579412edfe1
diff --git a/tests/malloc_test.cpp b/tests/malloc_test.cpp
index 30da5c3..f15fc75 100644
--- a/tests/malloc_test.cpp
+++ b/tests/malloc_test.cpp
@@ -55,10 +55,14 @@
 
 #define HAVE_REALLOCARRAY 1
 
-#else
+#elif defined(__GLIBC__)
 
 #define HAVE_REALLOCARRAY __GLIBC_PREREQ(2, 26)
 
+#elif defined(MUSL)
+
+#define HAVE_REALLOCARRAY 1
+
 #endif
 
 TEST(malloc, malloc_std) {
@@ -655,10 +659,14 @@
 }
 
 TEST(malloc, mallopt_smoke) {
+#if !defined(MUSL)
   errno = 0;
   ASSERT_EQ(0, mallopt(-1000, 1));
   // mallopt doesn't set errno.
   ASSERT_EQ(0, errno);
+#else
+  GTEST_SKIP() << "musl doesn't have mallopt";
+#endif
 }
 
 TEST(malloc, mallopt_decay) {