Link with $(CXX), not the build host g++.

diff -Nrup a/Makefile b/Makefile
--- a/Makefile	2004-04-12 14:02:33.000000000 +0200
+++ b/Makefile	2026-10-22 17:22:43.166514335 +0200
@@ -3,7 +3,7 @@ CPPFLAGS += -I. -fPIC -D_REENTRANT -Wall
 
 
 blvco.so:	blvco.o blvco_if.o exp2ap.o
-	g++ -shared  blvco.o blvco_if.o exp2ap.o -o blvco.so
+	$(CXX) -shared  blvco.o blvco_if.o exp2ap.o -o blvco.so
 
 blvco.o:	ladspaplugin.h blvco.h ladspa.h
 blvco_if.o:	ladspaplugin.h blvco.h ladspa.h