can not found mcp/mpfr/gmp, but i has installed them.

["刘 加权" <liujiaquan@ultrain.io>]

  cmd 1 : ./configure --disable-multilib  --prefix=/usr/local --with-mpc=/usr/local --with-mpfr=/usr/local --with-gmp=/usr/local &&  make -j4 && sudo make install
  cmd 2 : ./configure --disable-multilib  --prefix=/usr/local  &&  make -j4 && sudo make install

after I installed mpfr mpc  gmp , I use  --with-mpc=/usr/local to set the path,
but configure give me the error blew:

checking for the correct version of gmp.h... yes
checking for the correct version of mpfr.h... yes
checking for the correct version of mpc.h... yes
checking for the correct version of the gmp/mpfr/mpc libraries... no
configure: error: Building GCC requires GMP 4.2+, MPFR 2.4.0+ and MPC 0.8.0+.
Try the --with-gmp, --with-mpfr and/or --with-mpc options to specify
their locations.  Source code for these libraries can be found at
their respective hosting sites as well as at
ftp://gcc.gnu.org/pub/gcc/infrastructure/.  See also
http://gcc.gnu.org/install/prerequisites.html for additional info.  If
you obtained GMP, MPFR and/or MPC from a vendor distribution package,
make sure that you have installed both the libraries and the header
files.  They may be located in separate packages.


but I already installed  mpfr mpc and gmp into /usr/local directory, ls show like blew:

vi@linx:/usr/local$ ls
etc  games  gmssl  include  intranet_security  lib  man  sbin  share  src
vi@linx:/usr/local$ ls include/
gmp.h  libelf  mpc.h  mpf2mpfr.h  mpfr.h
vi@linx:/usr/local$ ls lib
libelf.a   libelf.so.0       libgmp.a   libgmp.so     libgmp.so.10.3.2  libmpc.la<http://libmpc.la>  libmpc.so.3      libmpfr.a   libmpfr.so    libmpfr.so.6.0.2  pkgconfig  python2.6
libelf.so  libelf.so.0.8.12  libgmp.la<http://libgmp.la>  libgmp.so.10  libmpc.a          libmpc.so  libmpc.so.3.1.0  libmpfr.la<http://libmpfr.la>  libmpfr.so.6  ocaml             python2.5  site_ruby
vi@linx:/usr/local$ pwd
/usr/local
vi@linx:/usr/local$


then I try configure without set mpc,mpfr and gmp location by use cmd 2: ./configure --disable-multilib  --prefix=/usr/local  &&  make -j4 && sudo make install
it gives me the right configure result and then I can run make to buid the gcc 7.3.0

I want to know the reason. and where is wrong? thank you very much, guys!

My system is Debian 6, codename is squeeze.