Add rationale for the MAP_ANONYMOUS vs. MAP_ANON flags.

llvm-svn: 7368
diff --git a/llvm/lib/ExecutionEngine/JIT/Emitter.cpp b/llvm/lib/ExecutionEngine/JIT/Emitter.cpp
index e6dc706..9e62f13 100644
--- a/llvm/lib/ExecutionEngine/JIT/Emitter.cpp
+++ b/llvm/lib/ExecutionEngine/JIT/Emitter.cpp
@@ -73,6 +73,7 @@
   static const long pageSize = sysconf(_SC_PAGESIZE);
 
 #if defined(i386) || defined(__i386__) || defined(__x86__)
+  /* Linux and *BSD tend to have these flags named differently. */
 #if defined(MAP_ANON) && !defined(MAP_ANONYMOUS)
 # define MAP_ANONYMOUS MAP_ANON
 #endif