sanitise sign comparisons

This is a mechanical change addressing the various sign comparison warnings that
are identified by both clang and gcc.  This helps cleanup some of the warning
spew that occurs during builds.

llvm-svn: 205390
diff --git a/lldb/source/DataFormatters/CF.cpp b/lldb/source/DataFormatters/CF.cpp
index a4b7a12..342ced7 100644
--- a/lldb/source/DataFormatters/CF.cpp
+++ b/lldb/source/DataFormatters/CF.cpp
@@ -160,7 +160,7 @@
     if (error.Fail() || num_bytes == 0)
         return false;
     uint8_t *bytes = buffer_sp->GetBytes();
-    for (int byte_idx = 0; byte_idx < num_bytes-1; byte_idx++)
+    for (uint64_t byte_idx = 0; byte_idx < num_bytes-1; byte_idx++)
     {
         uint8_t byte = bytes[byte_idx];
         bool bit0 = (byte & 1) == 1;