Silence -Wqual-cast warnings from GCC 5.2

There were a number of const qualifiers being cast away which caused warnings.
This cluttered the output hiding real errors.  Silence them by explicit casting.
NFC.

llvm-svn: 250662
diff --git a/lldb/source/Core/StreamString.cpp b/lldb/source/Core/StreamString.cpp
index ef2b705..36e086b 100644
--- a/lldb/source/Core/StreamString.cpp
+++ b/lldb/source/Core/StreamString.cpp
@@ -37,7 +37,7 @@
 size_t
 StreamString::Write (const void *s, size_t length)
 {
-    m_packet.append ((char *)s, length);
+    m_packet.append (reinterpret_cast<const char *>(s), length);
     return length;
 }