_AC_COMPILER_EXEEXT_CROSS: exit 77 if test program does not run

_AC_COMPILER_EXEEXT_CROSS: exit 77 if test program does not run

This causes our testsuite to report a skipped test, rather than a
failure, if the detected compiler for _AC_LANG produces broken
executables.  It matches the behavior of _AC_COMPILER_EXEEXT_DEFAULT,
which has exited with that code for a long time if it hits the
“_AC_LANG compiler cannot *create* executables” failure case.

Partially addresses bug #110267.  The Solaris 10 machine I have access
to, has a broken gccgo installation that generates executables that
crash on startup.   Without this patch, test “358: Go” fails.  With
this patch, it is skipped.