PTHREAD_CREATE_NULL_ARG2): Accomodate old pthreads implementations.
* gdb.threads/pthreads.exp: Try linking with both -lpthread (Solaris)
and -lpthreads (everybody else).
(test_startup): Fail gracefully if threads are not supported.
* gdb.base/nodebug.exp: Add setup_xfail hppa*-*-hpux* for
"p/c array_index("abcdef",2)" when not gcc compiled.
* gdb.base/corefile.exp: Add setup_xfail hppa*-*-hpux* for
"print func2::coremaker_local" when not gcc compiled.
* gdb.base/opaque.exp: Remove setup_xfail hppa*-*-hpux* for
"ptype on opaque struct tagname (statically)",
"ptype on opaque struct tagname (dynamically) 1", and
"ptype on opaque struct tagname (dynamically) 2"
for not compiled with gcc.
* gdb.base/mips_pro.exp: Only do setup_xfail hppa*-*-* for
backtrace when compiled with gcc.
* lib/gdb.exp (runto_main): Return result of "runto main" rather
than always return success.
