[toplevel] Overhaul detection of target compilers

[Paul Brook]

> 2005-07-14  Paolo Bonzini  <bonzini@gnu.org>
>
>         * configure.in (CC_FOR_TARGET, CXX_FOR_TARGET, GCJ_FOR_TARGET,
>         GCC_FOR_TARGET, RAW_CXX_FOR_TARGET, GFORTRAN_FOR_TARGET): Find
>         them with NCN_STRICT_CHECK_TARGET_TOOL, like the other target
>         tools; remove code to manually set them.
>         (Target tools): Look in the environment for them.
>         * Makefile.tpl (CC_FOR_TARGET, CXX_FOR_TARGET, GCJ_FOR_TARGET,
>         GCC_FOR_TARGET, RAW_CXX_FOR_TARGET, GFORTRAN_FOR_TARGET): Redefine.
>         (AS_FOR_TARGET, LD_FOR_TARGET, NM_FOR_TARGET): Look into gcc
>         build directory.
>         (CONFIGURED_CC_FOR_TARGET, CONFIGURED_CXX_FOR_TARGET,
>         CONFIGURED_GCJ_FOR_TARGET, CONFIGURED_GCC_FOR_TARGET,
>         CONFIGURED_GFORTRAN_FOR_TARGET, USUAL_CC_FOR_TARGET,
>         USUAL_CXX_FOR_TARGET, USUAL_GCJ_FOR_TARGET, USUAL_GCC_FOR_TARGET,
>         USUAL_RAW_CXX_FOR_TARGET, USUAL_GFORTRAN_FOR_TARGET): New.
>         (CXX_FOR_TARGET_FOR_RECURSIVE_MAKE,
>         RAW_CXX_FOR_TARGET_FOR_RECURSIVE_MAKE, RECURSE_FLAGS): Delete.
>         * configure: Regenerate.
>         * Makefile.in: Regenerate.

This breaks newlib cross builds. 

make[4]: arm-unknown-eabi-cc: Command not found
make[4]: *** [dummy.o] Error 127
make[4]: Leaving directory 
`/home/paul/arm/newlib/obj-eabi/arm-unknown-eabi/newlib/libc/argz'

It appears that toplevel configure is setting CONFIGURED_CC_FOR_TARGET to 
arm-unknown-eabi-cc even though this binary doesn't exist (only -gcc does), 
and this value then works its way up to $(CC) in newlib/

Paul