Don't keep appending to the current crash description with each formatted crash description call.

llvm-svn: 118703
diff --git a/lldb/source/Host/macosx/Host.mm b/lldb/source/Host/macosx/Host.mm
index c4f393d..b816fe1 100644
--- a/lldb/source/Host/macosx/Host.mm
+++ b/lldb/source/Host/macosx/Host.mm
@@ -554,6 +554,7 @@
     {
         va_list args;
         va_start (args, format);
+        g_crash_description.GetString().clear();
         g_crash_description.PrintfVarArg(format, args);
         va_end (args);
         __crashreporter_info__ = g_crash_description.GetData();