Check that pthread_mutex_init() works from ctor.

Based on problem report and test case from @liuw

tests/basic/misc_test.c

@@ -1,5 +1,6 @@
 #include <sys/times.h>
 
+#include <pthread.h>
 #include <stdio.h>
 
 #include <rumprun/tester.h>
@@ -21,20 +22,44 @@ static int
 test_times(void)
 {
 	struct tms tms;
-	
+
 	printf("checking that calling times() does not crash ... ");
 	times(&tms);
 	prfres(0);
 
 	return 0;
 }
 
+/*
+ * Check that pthread has been initialized when constructors are
+ * called.  Issue reported by @liuw on irc
+ */
+static pthread_mutex_t ptm;
+static void __attribute__((constructor))
+pthmtxinit(void)
+{
+
+	pthread_mutex_init(&ptm, NULL);
+}
+static int
+test_pthread_in_ctor(void)
+{
+	int rv;
+
+	printf("checking that pthread_mutex_init() works from ctor ... ");
+	rv = pthread_mutex_destroy(&ptm);
+	prfres(rv);
+
+	return rv;
+}
+
 int
 rumprun_test(int argc, char *argv[])
 {
 	int rv = 0;
 
 	rv += test_times();
+	rv += test_pthread_in_ctor();
 
 	return rv;
 }