Separate CFLAGS_SL and CXXFLAGS_SL, to allow building with C and C++

compilers from different providers.  (Especially important since the
C++ compiler that goes with your favourite C compiler might not work.)

src/makefiles/Makefile.unixware

@@ -7,6 +7,11 @@ CFLAGS_SL = -fpic
 else
 CFLAGS_SL = -K PIC
 endif
+ifeq ($(GXX), yes)
+CXXFLAGS_SL = -fpic
+else
+CXXFLAGS_SL = -K PIC
+endif
 
 %.so: %.o
 	$(LD) -G -Bdynamic -o $@ $<