configure: add --without-mdb flag

Add a configuration flag that prevents mdb_v8.so from being built.
The default behavior is still the same and mdb_v8.so is built by default
on Solaris based platforms such as SmartOS.

Using --without-mdb fixes build issues on Solaris based platforms where
libproc.h is not available or not compatible with the one shipped by
SmartOS.

Fixes #6439.

configure

@@ -282,6 +282,11 @@ parser.add_option('--without-etw',
     dest='without_etw',
     help='build without ETW')
 
+parser.add_option('--without-mdb',
+    action='store_true',
+    dest='without_mdb',
+    help='build without mdb')
+
 parser.add_option('--without-npm',
     action='store_true',
     dest='without_npm',
@@ -554,7 +559,7 @@ def configure_node(o):
   # if we're on illumos based systems wrap the helper library into the
   # executable
   if flavor == 'solaris':
-    o['variables']['node_use_mdb'] = 'true'
+    o['variables']['node_use_mdb'] = b(not options.without_mdb)
   else:
     o['variables']['node_use_mdb'] = 'false'