sudo apt -y install bridge-utils cpu-checker libvirt-clients libvirt-daemon qemu qemu-kvm xorriso mtools
sudo kvm-ok

# Should output
# INFO: /dev/kvm exists
# KVM acceleration can be used

export PREFIX="$HOME/opt/cross"
export TARGET=i686-elf
export PATH="$PREFIX/bin:$PATH"
export INSTALL_NUM_CORES=8

sudo apt install bison flex libgmp3-dev libmpc-dev libmpfr-dev  texinfo

mkdir CrossCompiler
cd    CrossCompiler

wget https://ftp.gnu.org/gnu/binutils/binutils-2.34.tar.gz
tar -xf binutils-2.34.tar.gz
rm      binutils-2.34.tar.gz

wget https://ftp.gnu.org/gnu/gcc/gcc-9.4.0/gcc-9.4.0.tar.gz
tar -xf gcc-9.4.0.tar.gz
rm      gcc-9.4.0.tar.gz

wget https://ftp.gnu.org/gnu/gdb/gdb-9.2.tar.gz
tar -xf gdb-9.2.tar.gz
rm gdb-9.2.tar.gz

cd CrossCompiler
 
mkdir build-binutils
cd build-binutils

../binutils-2.34/configure --target=$TARGET --prefix="$PREFIX" --with-sysroot --disable-nls --disable-werror
make         -j $INSTALL_NUM_CORES
make install -j $INSTALL_NUM_CORES

cd CrossCompiler
cd build-binutils

../gdb.9.2/configure --target=$TARGET --prefix="$PREFIX" --disable-werror
make all-gdb     -j $INSTALL_NUM_CORES
make install-gdb -j $INSTALL_NUM_CORES

cd CrossCompiler
 
which -- $TARGET-as || echo $TARGET-as is not in the PATH
 
mkdir build-gcc
cd build-gcc
../gcc-9.4.0/configure --target=$TARGET --prefix="$PREFIX" --disable-nls --enable-languages=c,c++ --without-headers
make all-gcc               -j $INSTALL_NUM_CORES
make all-target-libgcc     -j $INSTALL_NUM_CORES
make install-gcc           -j $INSTALL_NUM_CORES
make install-target-libgcc -j $INSTALL_NUM_CORES

❯ $HOME/opt/cross/bin/$TARGET-gcc --version
------------------------------------------------------------------------------
i686-elf-gcc (GCC) 9.4.0
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

export PATH="$HOME/opt/cross/bin:$PATH"

❯ which i686-elf-gcc
/home/joep/opt/cross/bin/i686-elf-gcc