macOS: sed -i portability blocks build (Makefile + nistcurves p384 staging) #34

macOS build aborts on sed -i calls in Makefile + tools/integration/

Symptom

Building on macOS sequoia (BSD sed) fails on the very first sed -i invocation with errors like:

sed: 1: "<file>": undefined label '<file>'

…or silently uses the file argument as the backup-suffix and corrupts the source tree, depending on which call fires first. GNU sed (Linux default) is happy with sed -i '<expr>' file; BSD sed (macOS default) requires sed -i '' '<expr>' file (explicit empty backup-suffix argument).

Affected files

tools/integration/build_nistcurves_p256.sh was already updated to use sed -i ''. Twelve more sites across three files still use the GNU-only form:

Fix

Convert each call site to the BSD-portable form sed -i '' '<expr>' file. GNU sed accepts the empty-string suffix argument as a no-op, so the change preserves Linux compatibility.

Out of scope (already resolved upstream)

While diagnosing this, I also looked at two other macOS-portability issues I had hit historically against c64-https@6c9d2a3 (Phase C.1):

1. tools/integration/build_x25519.sh had 7× sed -i sites — the script no longer exists on master after the Phase C.1 rollback, so this is moot.
2. tools/uci/test_https_local.py:_load_labels() used to crash on REU-overlay-bank label lines (no : in parts[1]). Master has replaced the inline parser with Labels.from_file() (c64-test-harness ≥0.12.4), which handles both C: and bank-prefixed forms — also moot.

A PR for the remaining 12 sites is incoming.