creating broken binaries..

[Ralf Wildenhues]

HPUX cc apparently leaves a broken, but non-executable binary with this
sequence (which causes fail.at to fail):

| $ echo 'int not_main() { return 0;}' > a.c
| $ cc -c a.c
| $ cc -o a a.o; echo $?
| ld: Unsatisfied symbol "main" in file <no file>
| 1 errors.
| 1
| $ nm a | grep main
| [60]     |            0|       0|NOTYP|GLOB |0|   UNDEF|main
| [52]     |     67110912|      16|FUNC |GLOB |0|   .text|not_main

Should libtool remove the output file in case the link line failed?
I'm a little bit wary of this, it may still be useful for the user?

Otherwise, we need to fix fail.at to use the same technique as
AS_EXECUTABLE_P, if we don't want to try to actually execute the binary.

Cheers,
Ralf