Disable info messages by default for malloc debug.

Add a new option verbose for malloc debug that is not enabled by default.
This disables all of the info log messages. It turns out these log
messages can add a measurable amount of time and can change the boot up.

Bug: 129239269

Test: Adjusted unit tests pass.
Test: Verified no messages unless verbose option used.
Change-Id: I805cb7c8ecb44de88119574e59d784877cacc383
diff --git a/libc/malloc_debug/malloc_debug.cpp b/libc/malloc_debug/malloc_debug.cpp
index 093bdee..1145796 100644
--- a/libc/malloc_debug/malloc_debug.cpp
+++ b/libc/malloc_debug/malloc_debug.cpp
@@ -30,6 +30,7 @@
 #include <inttypes.h>
 #include <malloc.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 #include <sys/cdefs.h>
 #include <sys/param.h>
@@ -252,6 +253,10 @@
   // of different error cases.
   backtrace_startup();
 
+  if (g_debug->config().options() & VERBOSE) {
+    info_log("%s: malloc debug enabled", getprogname());
+  }
+
   return true;
 }