buildscripts: make unix.sh and make_dependencies.sh arch aware (#4384)

ARCH can be '32' or '64'. If it is not set then default to '64'.

make_dependencies.sh should do the symlinking
diff --git a/.travis.yml b/.travis.yml
index 7ea9aee..9ed0023 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -17,8 +17,7 @@
     ln -s /tmp/gradle-wrapper $HOME/.gradle/wrapper
     # Work around https://github.com/travis-ci/travis-ci/issues/2317
   - if \[ "$TRAVIS_OS_NAME" = linux \]; then jdk_switcher use oraclejdk8; fi
-  - buildscripts/make_dependencies.sh # build protoc into /tmp/protobuf-${PROTOBUF_VERSION}
-  - ln -s "/tmp/protobuf-${PROTOBUF_VERSION}/$(uname -s)-$(uname -p)" /tmp/protobuf
+  - buildscripts/make_dependencies.sh # build protoc into /tmp/protobuf
   - mkdir -p $HOME/.gradle
   - echo "checkstyle.ignoreFailures=false" >> $HOME/.gradle/gradle.properties
   - echo "failOnWarnings=true" >> $HOME/.gradle/gradle.properties