gh-84461: Add HOSTRUNNER for program to run Python executable

[emmatyping]

HOSTRUNNER is a program which can be used to run BUILDPYTHON for the host platform (for example, python.js requires node).

Also change depedencies from build_all to all so that targets which can't build everything (e.g. WASM) can still run buildbottest and pythoninfo.

cc @tiran

Automerge-Triggered-By: GH:tiran

[tiran]

• Add [] around arguments.
• Fix whitespace / tab
• You need to AC_SUBST variables to make configure substitute the variable in templates.
• Threaded builds need additional arguments to enable experimental threading and shared buffers

AS_VAR_IF([enable_wasm_pthreads], [yes], [
HOSTRUNNER='node --experimental-wasm-threads --experimental-wasm-bulk-memory'
], [
HOSTRUNNER='node'
])