1、下载源吗：

wget http://mirrors.ustc.edu.cn/gnu/gcc/gcc-8.5.0/gcc-8.5.0.tar.gz

解压：

tar -xf gcc-8.5.0.tar.gz

cd gcc-8.5.0

2、下载依赖：mpc mpfr gmp isl

./contrib/download_prerequisites

编译mpc:

cd mpc

mkdir build

cd build

../configure --prefix=/usr/local/mpc

编译mpfr :

cd ../../mpfr 

mkdir build

cd build

../configure --prefix=/usr/local/mpfr 

编译gmp:

cd ../../gmp

mkdir build

cd build

../configure --prefix=/usr/local/gmp

编译isl:

cd ../../isl

mkdir build

cd build

../configure --prefix=/usr/local/isl

3、编译gcc

cd ../..

mkdir build

cd build 

../configure --prefix=/usr/local/gcc-8.5.0 --enable-languages=c,c++ --disable-multilib --with-abi=64 --with-mpfr=/usr/local/mpfr --with-mpc=/usr/local/mpc --with-mpfr=/usr/local/mpfr --with-isl=/usr/local/isl --with-gmp=/usr/local/gmp

make -j8

sudo make install