build not installing C libraries

[Alan Lehotsky <qsmgmt at earthlink dot net>]

I've set up a 'unified source tree' with 

binutils-2.21.1
gcc-4.6.1
newlib-1.19.0
gdb-7.2

for a new toolchain.  My configure looks like

mkdir -p ${build_dir} && cd ${build_dir} \
  && ../${unified_src}/configure --target=${PROC}-unknown-elf \
    --enable-fast-install=N/A \
    --with-newlib \
    --with-headers=../{unified_src}/newlib/libc/include \
    --with-gmp=/usr/local \
    --with-mpfr=/usr/local \
    --with-mpc=/usr/local \
    --enable-cgen-maint \
    --enable-sim \
    --enable-maintainer-mode \
    --enable-64-bit-bfd \
    --enable-target-optspace \
    --enable-languages=c,c++ --prefix=${install_dir}

The tree 'make's' successfully, but the resulting object-tree doesn't have any of the standard C library headers.  Doing a 

	make install

doesn't copy them out of the newlib/libc/include  subtree, and a

     cd gcc; make check-gcc

starts failing on every test that contains an 'include', starting with gcc.c-torture/execute/20000112-1.c asking for string.h

I've done previous ports using newlib (but it was a long time ago).  Any ideas where I should look for hints as to what's misconfigured?  There's a subdirectory tree

     $(build_dir)/$(PROC)-unknown-elf/newlib/targ-include

but all it has in it is newlib.h and empty bits, machine and sys subdirectories