No `python` in PATH in recent Linux distros

[Paul Hargrove]

With the EOL for python2, it appears that some Linux distros are now defaulting to installing /usr/bin/python3 without a /usr/bin/python symlink. They then also provide an optional package with /usr/bin/python2, but also without a /usr/bin/python symlink. I can attest first-hand that Ubuntu 20.04 is one distro with this behavior by default.

The net result is that python scripts to be used on such a distro must be explicit about python2 vs python3. UPC++ does not currently match this expectation and configure fails by default:

ERROR: Python interpreter 'python' was not found in $PATH.
Use '--with-python=...' to specify a Python interpreter.

[Paul Hargrove]

The obvious work-around (configure --with-python=python3) works as one would hope.

However, we can/should do better by looking for python3 or python2 in addition to bare python.

[Paul Hargrove]

Proposed solution in pull request 218

[Paul Hargrove]

configure: search PATH for python3 and python2

This commit resolves issue #373: "No python in $PATH in recent Linux distros" by adding python3 and python2 to the names searched for in $PATH at configure time.

→ <<cset f149db7532f0>>

[Dan Bonachea]

configure: search PATH for python3 and python2

This commit resolves issue #373: "No python in $PATH in recent Linux distros" by adding python3 and python2 to the names searched for in $PATH at configure time.

(cherry picked from commit f149db7532f00e640c0ca72104f84712f484ff8f)

Conflicts: configure

→ <<cset d59e7e0a8b3b>>