GCC install prerequisites for spack

package.py

# ./src/spack/var/spack/repos/builtin/packages/gcc/package.py

# https://gcc.gnu.org/install/prerequisites.html
    depends_on('gmp@4.3.2:')
    #depends_on('mpfr@2.4.2:')
    depends_on('mpfr@2.4.2:3.1.6')
    depends_on('mpc@0.8.1:', when='@4.5:')
    #depends_on('isl@0.14', when='@5:5.9')
    depends_on('isl@0.15', when='@5:5.9')
    #depends_on('isl@0.15:', when='@6:')
    depends_on('isl@0.15:0.18', when='@6:8.9')
    depends_on('isl@0.15:0.20', when='@9:') ##
    depends_on('zlib', when='@6:')
    depends_on('gnat', when='languages=ada')
    depends_on('binutils~libiberty', when='+binutils')
    depends_on('zip', type='build', when='languages=java')