Don't call SBDebugger::SetInternalVariable in the sigwinch_handler, since that...

Don't call SBDebugger::SetInternalVariable in the sigwinch_handler, since that takes locks and potentially does allocations.
Just call SBDebugger::SetTerminalWidth on the driver's SBDebugger, which does the same job, but no locks.
Also add the value checking to SetTerminalWidth you get with SetInternalVariable(..., "term-width", ...).

rdar://problem/11310563

llvm-svn: 155665