v3.10
build: add libraries
build: update gnulib submodule to latest
cmp: avoid macros in cmp.c
diff: prefer nullptr to NULL
diff: use C23 bool
diff: avoid macros in diff.c
build: fix a new syntax-check failure
diff3: avoid macros in diff3.c
maint: update copyright dates
diff: avoid a macro in diff.h
sdiff: avoid some macros in sdiff.c