lang/gcc11: build with clang on powerpc64le

Copy the patch used for other gcc versions.

lang/gcc11/Makefile

@@ -64,9 +64,6 @@ CONFIGURE_ENV+=	UNAME_m="powerpc64"
 CONFIGURE_ARGS+=	--with-abi=elfv2
 . endif
 USE_GCC=	yes
-
-.elif ${ARCH} == powerpc64le
-USE_GCC=	yes
 .endif
 
 LANGUAGES:=	c,c++,objc,fortran,jit

lang/gcc11/files/patch-clang-vec_step

@@ -0,0 +1,21 @@
+https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=239266 reports how
+clang unfortunately poisons user namespace by default (without any
+special options).
+
+Until that changes (or GCC changes) we need to avoid using vec_step
+as a variable.
+
+--- UTC
+Index: gcc/tree-vect-loop.c
+===================================================================
+--- gcc/tree-vect-loop.c	(revision 273856)
++++ gcc/tree-vect-loop.c	(working copy)
+@@ -55,6 +55,8 @@ along with GCC; see the file COPYING3.  If not see
+ #include "vec-perm-indices.h"
+ #include "tree-eh.h"
+
++#define vec_step vec_step_
++
+ /* Loop Vectorization Pass.
+
+    This pass tries to vectorize loops.