`objtool` warnings

[rountree]

Building the tip of main using gcc 13.3.1 and kernel 4.18.0-553.74.1.1toss.t4.x86_64 results in:

./msr-safe/.tmp_msr_allowlist.o: warning: objtool: write_allowlist() falls through to next function write_allowlist.cold()
./msr-safe/.tmp_msr_allowlist.o: warning: objtool: write_allowlist.cold() falls through to next function write_allowlist()

This does not appear using gcc 15.2.0 and kernel 6.14.0-32-generic (Ubuntu Questing Quokka).