Better diagnostics when an anonymous mmap fails.

Change-Id: I0657950077c58c28b4f63990e42df6396215c07c
diff --git a/src/mem_map.cc b/src/mem_map.cc
index 9943343..ba34d8b 100644
--- a/src/mem_map.cc
+++ b/src/mem_map.cc
@@ -176,7 +176,8 @@
 
   byte* actual = reinterpret_cast<byte*>(mmap(addr, page_aligned_size, prot, flags, fd.get(), 0));
   if (actual == MAP_FAILED) {
-    PLOG(ERROR) << "mmap failed (" << name << ")";
+    PLOG(ERROR) << "mmap(" << reinterpret_cast<void*>(addr) << ", " << page_aligned_size
+                << ", " << prot << ", " << flags << ", " << fd.get() << ", 0) failed for " << name;
     return NULL;
   }
   return new MemMap(actual, length, actual, page_aligned_size);