lib/malloca.c: warning about [-Wsign-compare]

[Bjarni Ingi Gislason]

  Compilation with

Debian clang version 14.0.6-2
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

Software: groff (git HEAD)

  CC       lib/libgnu_a-malloca.o
../lib/malloca.c:54:38: warning: comparison of integers of different
signs: 'unsigned long' and 'idx_t' (aka 'long') [-Wsign-compare]
  if (!ckd_add (&nplus, n, plus) && !xalloc_oversized (nplus, 1))
                                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~
../lib/xalloc-oversized.h:62:33: note: expanded from macro 'xalloc_oversized'
# define xalloc_oversized(n, s) __xalloc_oversized (n, s)
                                ^~~~~~~~~~~~~~~~~~~~~~~~~
../lib/xalloc-oversized.h:33:8: note: expanded from macro '__xalloc_oversized'
       < (n)))
       ^  ~
1 warning generated.