[tamnd]

This change explains the section and table differences that the 7.3 compare on #110 reported with no reason. I read each one against the source and against a test compile on server3.

What changes

• .note.gnu.property only in the gcc objects of arch/x86/boot/compressed and drivers/firmware/efi/libstub. Ubuntu's gcc turns on -fcf-protection when no -fcf-protection is given, and writes the IBT and SHSTK note. These directories set their own flags without -fcf-protection. Debian's gcc and rucc write no note then. I checked this with gcc and rucc on a file with no flags. The EFI stub removes the note from each object.
• .text.startup only in the gcc objects of arch/x86/boot/main.o and arch/x86/realmode/rm/wakemain.o. gcc puts main there when it optimizes. Both linker scripts collect .text.*.
• The __bug_table site for WARN_ON(!ws) in wakeup_source_remove. Its only caller calls it inside if (ws), so rucc is correct to remove it.
• .altinstructions, .altinstr_replacement and .discard.annotate_data only in the gcc fs/super.o when CONFIG_BUG is off. rucc deletes the popcnt alternative of hweight32 because no one reads its result. gcc keeps it because of the ASM_CALL_CONSTRAINT output on the stack pointer. The result is the same here, but in general this is a difference from GCC, so I opened Keep an asm that writes a global register variable, as gcc does with ASM_CALL_CONSTRAINT rucc#3764 with a reduction.

Check

cargo test -p rk passes, and the file parses. The kernel workflow on this PR runs the compare again on 7.3.

Part of #109.