Search the system path for `program` in `launch.json`

Type: Feature Request

I currently have a launch.json set up for debugging a native Node.js addon on both Linux and OS X with gdb and llvm. Debugging a Node.js addon requires loading the main node executable which in turn dynamically loads the addon which is a shared library. So I have:

"type": "cppdbg",
"request": "launch",
"program": "/usr/bin/node",

which requires the full path to the program being debugged. Both gdb and llvm search the system path when invoking gdb node or llvm node, however the VSCode debugger does not invoke them as it checks that program exists.
Here is my full launch.json - https://github.com/mmomtchev/node-gdal-async/blob/master/.vscode/launch.json

Start with the launch.json configuration shown in the issue and trace how the cppdbg launch flow validates its program value before starting gdb or llvm. Done means a program name such as node can be accepted and resolved through the system path instead of requiring an absolute path.