How can I set path of vim from the shell command result

Question

I'd like to set c++ header file path automatically from .vimrc. So I tried to write .vimrc file as shown below:

let g:gcpp_headers_path=system("g++ --version | grep g++ | awk '{print \"/usr/include/c++/\"$NF}'")

"if isdirectory(gcpp_headers_path)
  set path+=g:gcpp_headers_path
"endif

from the vimrc above I found the vim variable path set as shown below:

:set path?
path=.,/usr/include,,,g:gcpp_headers_path

The wanted output is as shown below:

:set path?
path=.,/usr/include,/usr/include/c++/7.5.0

I'd like to get this reviewed. Could someone advise me?

F.Y.I. The command in system() is shown below:

~$ g++ --version | grep g++ | awk '{print "/usr/include/c++/"$NF}'
/usr/include/c++/7.5.0

For documentation I am writing my answer found here:

let g:gcpp_headers_path = system("g++ --version | grep g++ | awk '{print \"/usr/include/c++/\"$NF}'")

execute 'set path+=' . g:gcpp_headers_path

My vim version is Vi IMproved 8.0 (2016 Sep 12, compiled Jan 20 2022 02:47:53)

I raised new post for Windows