Mutex usage testing: set up wrapper functions

When using pthread mutexes (MBEDTLS_THREADING_C and
MBEDTLS_THREADING_PTHREAD enabled), and when test hooks are
enabled (MBEDTLS_TEST_HOOKS), set up wrappers around the
mbedtls_mutex_xxx abstraction. In this commit, the wrapper functions
don't do anything yet.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Signed-off-by: Chris Jones <christopher.jones@arm.com>
diff --git a/tests/suites/host_test.function b/tests/suites/host_test.function
index 1178135..3f8a945 100644
--- a/tests/suites/host_test.function
+++ b/tests/suites/host_test.function
@@ -412,6 +412,10 @@
     mbedtls_memory_buffer_alloc_init( alloc_buf, sizeof( alloc_buf ) );
 #endif
 
+#if defined(MBEDTLS_TEST_MUTEX_USAGE)
+    mbedtls_test_mutex_usage_init( );
+#endif
+
     /*
      * The C standard doesn't guarantee that all-bits-0 is the representation
      * of a NULL pointer. We do however use that in our code for initializing