Provide a definition of CPP for gen-params that works with DESTDIR.

gnu/lib/libstdc++/config/Makefile

@@ -1,4 +1,4 @@
-#	$NetBSD: Makefile,v 1.1 1998/08/28 15:31:29 tv Exp $
+#	$NetBSD: Makefile,v 1.2 1999/02/11 18:20:58 tv Exp $
 
 # Makefile for _G_config.h, a machine-dependent automatically generated
 # configuration file.
@@ -12,6 +12,7 @@ DIST=		${.CURDIR}/../../../dist
 
 _G_config.h: Makefile ${DIST}/libio/gen-params
 	rootme=${.OBJDIR} CC="${CC}" CXX="${CXX}" CONFIG_NM="${NM}" \
+	    CPP="${CC} -E -nostdinc -idirafter ${DESTDIR}/usr/include" \
 	    /bin/sh ${DIST}/libio/gen-params LIB_VERSION=2.9.0 >$@
 
 all: ${DPSRCS}