Include <threads.h> if it exists

configure.ac

@@ -658,7 +658,7 @@ AC_SUBST(CFLAGS_RDRAND)
 
 AC_CHECK_HEADERS([sys/mman.h sys/param.h sys/random.h intrin.h sys/auxv.h])
 AC_CHECK_HEADERS([CommonCrypto/CommonRandom.h])
-AC_CHECK_HEADERS([cet.h])
+AC_CHECK_HEADERS([cet.h threads.h])
 
 AC_MSG_CHECKING([if _xgetbv() is available])
 AC_LINK_IFELSE(

src/libsodium/randombytes/internal/randombytes_internal_random.c

@@ -9,6 +9,9 @@
 #if !defined(_MSC_VER) && !defined(__BORLANDC__)
 # include <unistd.h>
 #endif
+#if !defined(__STDC_NO_THREADS__) && defined(HAVE_THREADS_H)
+# include <threads.h>
+#endif
 
 #include <sys/types.h>
 #ifndef _WIN32