clang on powerpc64 defines vec_step already which collides with the
symbol in gcc, see https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=239266#c23
renaming suggested at https://gcc.gnu.org/legacy-ml/gcc/2019-07/msg00131.html

Index: gcc/tree-vect-transform.c
--- gcc/tree-vect-transform.c.orig
+++ gcc/tree-vect-transform.c
@@ -46,6 +46,8 @@ along with GCC; see the file COPYING3.  If not see
 #include "toplev.h"
 #include "real.h"
 
+#define vec_step vec_step_
+
 /* Utility functions for the code transformation.  */
 static bool vect_transform_stmt (gimple, gimple_stmt_iterator *, bool *,
 				 slp_tree, slp_instance);