missing check for malloc NULL result

[Bruno Haible]

Hi,

At these places malloc/realloc/calloc NULL results are not well handled, IIUC.

Sergey:
  argp-help.c:440
  argp-help.c:463
  argp-help.c:464
  argp-help.c:877
  argp-help.c:880
Simon:
  gc-gnulib.c:583
Jim:
  hash.c:578
Paul:
  regcomp.c:864
  regcomp.c:3030 missing cleanup action, leaks memory
  regcomp.c:3570 missing cleanup action, leaks memory
  regexec.c:3392

Bruno