[sparc64/base-gcc] Fix build of math/py-scikit-learn

py-scikit-learn uses C++11, so base-gcc doesn't work to build it.

This fixes the build on sparc64.

ok?

(cc maintiainer)

--Kurt

Index: Makefile
===================================================================
RCS file: /cvs/ports/math/py-scikit-learn/Makefile,v
retrieving revision 1.8
diff -u -p -r1.8 Makefile
--- Makefile 28 Oct 2020 04:04:04 -0000 1.8
+++ Makefile 13 Nov 2020 21:14:20 -0000
@@ -15,6 +15,9 @@ MAINTAINER = Paul Irofti <paul@irofti.n
# BSD-3
PERMIT_PACKAGE = Yes

+# C++11
+COMPILER = base-clang ports-gcc
+
WANTLIB += ${COMPILER_LIBCXX} m

MODULES = lang/python