build: fix mkpeephole configuration

mkpeephole is a binary that gets generated and run at V8 build time.
On cross-compilation builds separate build toolchains are required.
Similar to want_separate_host_toolset we default to disabled.

PR-URL: https://github.com/nodejs/node/pull/8317
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

configure

@@ -760,6 +760,8 @@ def configure_node(o):
   want_snapshots = not options.without_snapshot
   o['variables']['want_separate_host_toolset'] = int(
       cross_compiling and want_snapshots)
+  o['variables']['want_separate_host_toolset_mkpeephole'] = int(
+      cross_compiling)
 
   if target_arch == 'arm':
     configure_arm(o)