Shell crash on SunOS 4.1.3

[Torbjorn Granlund]

Running configure from the current GMP working sources,
SunOS 4.1.3 /bin/sh catches a segfault.

I tracked down the problem to some lines in the newly generated
config.status:

  # If the user did not use the arguments to specify the items to instantiate,
  # then the envvar interface is used.  Set only those that are not.
  if $ac_need_defaults; then
    CONFIG_FILES=${CONFIG_FILES="$config_files"}
    CONFIG_HEADERS=${CONFIG_HEADERS="$config_headers"}
    CONFIG_LINKS=${CONFIG_LINKS="$config_links"}
    CONFIG_COMMANDS=${CONFIG_COMMANDS="$config_commands"}
  fi

The crash happens on the 2nd line after `then'.  Adding `set -x' to
config.status yield this output (last lines):

ac_need_defaults=:
+ test 0 != 0 
+ : 
CONFIG_FILES=Makefile mpf/Makefile mpz/Makefile mpn/Makefile mpq/Makefile   
mpf/tests/Makefile mpz/tests/Makefile mpq/tests/Makefile mpn/tests/Makefile   
tests/Makefile tests/rand/Makefile demos/Makefile tune/Makefile   
mpbsd/Makefile mpbsd/tests/Makefile mpfr/Makefile mpfr/tests/Makefile
CONFIG_HEADERS= config.h:config.in

Has anybody encountered a similar problem before?  I weird workaround
is to instatiate ac_need_defaults to `true' instead of `:'.  Also,
just inserting a `true' or `:' after `then' helps.

(Yes, SunOS 4.1.3 is an obsolete version of an obsolete OS, but I'd
like to support GNU MP even on such systems if possible.)

--
Torbjörn