run_python.sh: Add readlink to allow symlinks to compiler entry points to work correctly

[kapouer]

This allows symbol links to the the compiler to work. Without this change, if you have for example /usr/bin/emcc as a symlink for /usr/local/share/emscripten/emcc then it would not work.

Fixes: #27211

[sbc100]

I updated the PR description, please can you check that I got that it right?

[sbc100]

(also updated the title.. again, please check I'm correct)

[sbc100]

It looks like there are a couple of valid failures on the arm64 macos bot:

/Users/distiller/emsdk/python/3.13.3_64bit/bin/python3: can't open file '/private/var/folders/vg/ldc8ffjj6ssdmh4txpd6tlf40000gn/T/emtest_4910fhtz/emscripten_test_other_v5ipcie4/.py': [Errno 2] No such file or directory
None
None
  test_toolchain_profiler (test_other.other.test_toolchain_profiler) ... FAIL (0.000s)
-- Looking for strtod - found

[sbc100]

Ah, the problem is the -f flag is not support on macOS readlink.

According to Gemini:

If the goal is to allow $0 to be executed via a symlink (e.g., from /usr/local/bin/emprofile ), the standard POSIX / macOS-safe way
to resolve $0 without relying on readlink -f is:

# Fallback to $0 if readlink fails (i.e. when $0 is a regular file)
TARGET=$(readlink "$0" 2>/dev/null || echo "$0")
exec "$_EM_PY" -E "$(dirname "$TARGET")/tools/emprofile.py" "$@"

[sbc100]

You also need to update tools/maint/run_python_compiler.sh I think