Update comments in binary build script

Misc comment fixes/improvements.

builds/build_python_runtime.sh

@@ -104,12 +104,12 @@ CONFIGURE_OPTS=(
   "--enable-optimizations"
   # Make autoconf's configure option validation more strict.
   "--enable-option-checking=fatal"
-  # Install Python into `/app/.heroku/python` rather than the default of `/usr/local`.
+  # Install Python into `/tmp/python` rather than the default of `/usr/local`.
   "--prefix=${INSTALL_DIR}"
   # Skip running `ensurepip` as part of install, since the buildpack installs a curated
   # version of pip itself (which ensures it's consistent across Python patch releases).
   "--with-ensurepip=no"
-  # Build the `pyexpat` module using the `expat` library in the stack image (which will
+  # Build the `pyexpat` module using the `expat` library in the base image (which will
   # automatically receive security updates), rather than CPython's vendored version.
   "--with-system-expat"
 )
@@ -125,6 +125,7 @@ if [[ "${PYTHON_MAJOR_VERSION}" != 3.[8-9] ]]; then
     #
     # However, shared builds are slower unless `no-semantic-interposition`and LTO is used:
     # https://fedoraproject.org/wiki/Changes/PythonNoSemanticInterpositionSpeedup
+    # https://github.com/python/cpython/issues/83161
     #
     # It's only as of Python 3.10 that `no-semantic-interposition` is enabled by default,
     # so we only use shared builds on Python 3.10+ to avoid needing to override the default
@@ -133,6 +134,7 @@ if [[ "${PYTHON_MAJOR_VERSION}" != 3.[8-9] ]]; then
     "--with-lto"
     # Counter-intuitively, the static library is still generated by default even when
     # the shared library is enabled, so we disable it to reduce the build size.
+    # This option only exists for Python 3.10+.
     "--without-static-libpython"
   )
 fi