During the exp-run in PR 208158, it was found that audio/ardour gives errors

with libc++ 3.8.0.  This is because the std::map's allocator was not defined
correctly.  Fix the `fast_pool_allocator' definition to use a `const double'.

PR:		209332
Submitted by:	dim

audio/ardour/Makefile

@@ -67,6 +67,8 @@ MAKE_ARGS+=	FPU_OPTIMIZATION=0
 post-patch:
 	@${REINPLACE_CMD} -e 's|%%CFLAGS%%|${CFLAGS}|' ${WRKSRC}/SConstruct
 	@${REINPLACE_CMD} -e 's|alsa_pcm|oss|g' ${WRKSRC}/templates/*.template
+	@${REINPLACE_CMD} -e 's|std::pair<double|std::pair<const double|' \
+		${WRKSRC}/gtk2_ardour/tempo_lines.h
 
 post-install:
 	@${MKDIR} ${STAGEDIR}${PREFIX}/share/ardour2/templates