set path=( /bin /usr/bin /sbin /usr/sbin /usr/local/bin )

env                                             \
        LANGS=c,c++,fortran,lto,objc,obj-c++    \
        CC=gcc6                                 \
        CXX=g++6                                \
        prefix=$prefix                          \
        BUILDPATH=$PATH                         \
        GMPPREFIX=$L/gmp                        \
        $G/gcc/build-dgcc.sh gcc-7-20171109

------------------------------------------------------------------------

The build-dgcc.sh script reports:

        nice time env CC="gcc6"                                                 \
                      CXX="g++6"                                                \
                      CFLAGS=""                                                 \
                      CPPFLAGS=""                                               \
                      CXXFLAGS=""                                               \
                      LDFLAGS="-L$L/lib64 -Wl,-rpath,$L/lib64"                  \
                ../gcc-7-20171109/configure                                     \
                        --disable-nls                                           \
                        --enable-decimal-float=dpd                              \
                        --enable-languages=c,c++,fortran,lto,objc,obj-c++       \
                        --with-gmp=$L/gmp                                       \
                        --with-mpfr=$L/gmp                                      \
                        --with-mpc=$L/gmp                                       \
                        --prefix=$L/ashare/gcc/gcc-7-20171109                   \
                        --libdir=$L/ashare/gcc/gcc-7-20171109/lib               &&
        nice time $L/bin/gnumake -j6 bootstrap