diff -u -r ../ddrescue-1.23/configure ./configure
--- ../ddrescue-1.23/configure	2018-02-13 12:54:43.000000000 +0000
+++ ./configure	2018-02-18 21:07:51.862861331 +0000
@@ -15,23 +15,15 @@
 LC_ALL=C
 export LC_ALL
 srcdir=
-prefix=/usr/local
+prefix?=/usr/local
 exec_prefix='$(prefix)'
 bindir='$(exec_prefix)/bin'
 datarootdir='$(prefix)/share'
 infodir='$(datarootdir)/info'
 mandir='$(datarootdir)/man'
-CXX=g++
+CXX?=g++
 CPPFLAGS=
-CXXFLAGS='-Wall -W -O2'
-LDFLAGS=
-
-# checking whether we are using GNU C++.
-/bin/sh -c "${CXX} --version" > /dev/null 2>&1 ||
-	{
-	CXX=c++
-	CXXFLAGS=-O2
-	}
+CXXFLAGS?='-Wall -W -O2'
 
 # Loop over all args
 args=