Use somewhat longer C++ program to detect whether linking requires the C++

compiler. Fixes #559429. 2.2 bugfix candidate.

configure

 #! /bin/sh
-# From configure.in Revision: 1.317 .
+# From configure.in Revision: 1.318 .
 # Guess values for system-dependent variables and create Makefiles.
 # Generated by GNU Autoconf 2.53.
 #
@@ -3037,7 +3037,7 @@ then
         if test -z "$CXX"; then
               LINKCC="\$(PURIFY) \$(CC)"
         else
-              echo 'int main(){return 0;}' > conftest.$ac_ext
+              echo 'void foo();int main(){foo();}void foo(){}' > conftest.$ac_ext
               $CXX -c conftest.$ac_ext 2>&5
               if $CC -o conftest$ac_exeext conftest.$ac_objext 2>&5 \
                  && test -s conftest$ac_exeext && ./conftest$ac_exeext

configure.in

@@ -309,7 +309,7 @@ then
         if test -z "$CXX"; then
               LINKCC="\$(PURIFY) \$(CC)"
         else
-              echo 'int main(){return 0;}' > conftest.$ac_ext
+              echo 'void foo();int main(){foo();}void foo(){}' > conftest.$ac_ext
               $CXX -c conftest.$ac_ext 2>&5
               if $CC -o conftest$ac_exeext conftest.$ac_objext 2>&5 \
                  && test -s conftest$ac_exeext && ./conftest$ac_exeext