Can't install pvl8 v.2.3.15: Regenerating ninja files - FAILED: build.ninja - linux-mint

Question

Linux Mint 20.2 , kernel 5.11.0-25-generic
I want to install plv8-2.3.15
Help here:
https://github.com/plv8/plv8/blob/v2.3.15/docs/BUILDING.md
Installed the next packages:
sudo apt-get update
sudo apt install git
sudo apt install python2
sudo apt install g++
sudo apt install pkg-config
sudo apt install libc-dev-bin
sudo apt install libc++abi-dev
sudo apt-get install libc++abi-dev
sudo apt install libc++-dev
sudo apt install libglib2.0-dev-bin
sudo apt install libtinfo5
sudo apt install ninja-build
Steps:
After make I get the next result:
./generate_upgrade.sh 2.3.15
sed -e 's/#PLV8_VERSION#/2.3.15/g' plv8.control.common | g++ -E -P -DLANG_plv8 - > plv8.control
sed -e 's/#LANG_NAME#/plv8/g' plv8.sql.common | sed -e 's/#PLV8_VERSION#/2.3.15/g' | g++ -E -P -I. -I./ -I/usr/include/postgresql/9.6/server -I/usr/include/postgresql/internal -Wdate-time -D_FORTIFY_SOURCE=2 -D_GNU_SOURCE -I/usr/include/libxml2 -I/usr/include/mit-krb5 -DLANG_plv8 - > plv8--2.3.15.sql
sed -e 's/#PLV8_VERSION#/2.3.15/g' plv8.control.common | g++ -E -P -DLANG_plcoffee - > plcoffee.control
sed -e 's/#LANG_NAME#/plcoffee/g' plv8.sql.common | sed -e 's/#PLV8_VERSION#/2.3.15/g' | g++ -E -P -I. -I./ -I/usr/include/postgresql/9.6/server -I/usr/include/postgresql/internal -Wdate-time -D_FORTIFY_SOURCE=2 -D_GNU_SOURCE -I/usr/include/libxml2 -I/usr/include/mit-krb5 -DLANG_plcoffee - > plcoffee--2.3.15.sql
sed -e 's/#PLV8_VERSION#/2.3.15/g' plv8.control.common | g++ -E -P -DLANG_plls - > plls.control
sed -e 's/#LANG_NAME#/plls/g' plv8.sql.common | sed -e 's/#PLV8_VERSION#/2.3.15/g' | g++ -E -P -I. -I./ -I/usr/include/postgresql/9.6/server -I/usr/include/postgresql/internal -Wdate-time -D_FORTIFY_SOURCE=2 -D_GNU_SOURCE -I/usr/include/libxml2 -I/usr/include/mit-krb5 -DLANG_plls - > plls--2.3.15.sql
Nice.
Now I want to install.
Try this
sudo make install
But I get error:
sudo make install
cd build/v8 ; env CXXFLAGS=-fPIC CFLAGS=-fPIC ninja -C out.gn/x64.release d8
ninja: Entering directory `out.gn/x64.release'
[1/1] Regenerating ninja files
FAILED: build.ninja
/home/Downloads/plv8-2.3.15/build/v8/buildtools/linux64/gn --root=/home/alexei/Downloads/plv8-2.3.15/build/v8 -q --check gen .
/bin/sh: 1: /home/alexei/Downloads/plv8-2.3.15/build/v8/buildtools/linux64/gn: not found
ninja: error: rebuilding 'build.ninja': subcommand failed
make: *** [Makefile:42: v8] Error 1