Failed to Build Boost With devtoolsets-8-gcc?

I tried to build Boost 1.71.0:

sudo ./bootstrap.sh --prefix=/opt/boost -with-toolset=gcc

And it gave:

Building Boost.Build engine with toolset gcc... 
Failed to build Boost.Build build engine
Consult 'bootstrap.log' for more details
$ cat bootstrap.log 
B2_TOOLSET is gcc, but the 'gcc' command cannot be executed.
Make sure 'gcc' is in PATH, or use a different toolset.

However, gcc is indeed in PATH:

$ which gcc
/opt/rh/devtoolset-8/root/usr/bin/gcc
$ echo $PATH
/opt/rh/devtoolset-8/root/usr/bin:/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin:/home/hc/.local/bin:/home/hc/bin

I wonder what goes wrong.

Thanks.