libc/uClibc: fix building on system with recent glibc

While trying to build a toolchain with ct-ng 1.5.0,
arm-unknown-linux-uclibcgnueabi target,
I get the following error:

[INFO ] Installing C library headers
[EXTRA] Copying sources to build dir
[EXTRA] Applying configuration
[EXTRA] Building headers
[EXTRA] Installing headers
[ERROR] extra/scripts/unifdef.c:209: error: conflicting types for 'getline'
[ERROR] make[2]: *** [extra/scripts/unifdef] Error 1
[ERROR] Build failed in step 'Installing C library headers'

The following patch solves the problem.
(It's a backport of this uClibc commit:
http://git.uclibc.org/uClibc/commit/?id=49e81cada73616864b9b31df0aeb6961c30f5a6e
)

[--SNIP from another mail--]
AFAIK this is a problem since glibc 2.10.

Correctly check for g++ existence.

Copyright 2007 Yann E. MORIN <yann.morin.1998@anciens.enib.fr>

Licensed to you as dmalloc-5.5.2 is.

diff -dur dmalloc-5.5.2.orig/configure dmalloc-5.5.2/configure

--- dmalloc-5.5.2.orig/configure	2007-05-18 11:40:31.000000000 +0200

+++ dmalloc-5.5.2/configure	2007-05-18 11:42:02.000000000 +0200

@@ -2643,7 +2643,7 @@

 # see if we actually have a CXX program

-if test "$ac_cv_prog_CXX" = "" -o ! -x "$ac_cv_prog_CXX"; then

+if test "$ac_cv_prog_CXX" = "" -o ! -x `which "$ac_cv_prog_CXX"`; then

     { echo "$as_me:$LINENO: WARNING: could not find C++ compiler $ac_cv_prog_CXX" >&5

 echo "$as_me: WARNING: could not find C++ compiler $ac_cv_prog_CXX" >&2;}

     enable_cxx=no