Add PROTOBUF_PRAGMA_INIT_SEG to protobuf.cfg (#7243)

The value of this appears to be effecting the exectuable layout, so
settings its value to an empty string should be fine.

It appears when generating protobuf sources sometimes.

Co-authored-by: Artemis Meursault Gerrard <[email protected]>

Author: artemis-gerrard-oxa

cfg/protobuf.cfg

@@ -1,5 +1,6 @@
 <?xml version="1.0"?>
 <def format="2">
+  <define name="PROTOBUF_PRAGMA_INIT_SEG" value=""/>
   <define name="PROTOBUF_VERSION" value="9999999"/>
   <define name="PROTOBUF_MIN_PROTOC_VERSION" value="0"/>
   <define name="PROTOBUF_NAMESPACE_OPEN" value=""/>