Add netbsd support to gyp build.

src/d8.gyp

Index: src/d8.gyp
diff --git a/src/d8.gyp b/src/d8.gyp
index bdc23a20e99b3a8ac69a91350c458f944f9f9271..a096af35b83f67aa5a15c198052fa813aa48b411 100644
--- a/src/d8.gyp
+++ b/src/d8.gyp
@@ -64,8 +64,8 @@
               'libraries': [ '-lreadline', ],
               'sources': [ 'd8-readline.cc' ],
             }],
-            [ '(OS=="linux" or OS=="mac" or OS=="freebsd" \
-              or OS=="openbsd" or OS=="solaris" or OS=="android")', {
+            ['(OS=="linux" or OS=="mac" or OS=="freebsd" or OS=="netbsd" \
+               or OS=="openbsd" or OS=="solaris" or OS=="android")', {
               'sources': [ 'd8-posix.cc', ]
             }],
             [ 'OS=="win"', {