This fixes the following build error:

oldpwd=`pwd` && cd .../protobuf/src && \
$oldpwd/js_embed google/protobuf/compiler/js/well_known_types/any.js google/protobuf/compiler/js/well_known_types/struct.js google/protobuf/compiler/js/well_known_types/timestamp.js > $oldpwd/google/protobuf/compiler/js/well_known_types_embed.cc
/bin/bash: line 1: .../protobuf/target/src/google/protobuf/compiler/js/well_known_types_embed.cc: No such file or directory
Makefile:8201: recipe for target 'google/protobuf/compiler/js/well_known_types_embed.cc' failed

which is observed during the cross-compilation since the version 3.2.