i*86-*-linux* xfails for "backtrace through signal handler".
* gdb.base/corefile.exp: Add i*86-*-sysv4* xfail for
"print func2::coremaker_local".
* gdb.base/break.exp: Add i*86-*-sysv4*, sparc-sun-sunos4,
xfail for
"delete all breakpoints when none".