Add top level build script for building packages.

ports/ruby_ppapi/build.sh

Index: ports/ruby_ppapi/build.sh
diff --git a/ports/ruby_ppapi/build.sh b/ports/ruby_ppapi/build.sh
old mode 100755
new mode 100644
index a87bbec6ee018ed048ea0a9dcbdd1ce8ebc48e87..19d0d3656651c194012f2e0001b57bddff5b1661
--- a/ports/ruby_ppapi/build.sh
+++ b/ports/ruby_ppapi/build.sh
@@ -3,15 +3,14 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-source pkg_info
-source ../../build_tools/common.sh
+BUILD_DIR=${START_DIR}
 
 BuildStep() {
   # The sample is built using the NaCl SDK common.mk system.
   # We override $(OUTBASE) to force the build system to put
   # all its artifacts in ${NACL_PACKAGES_REPOSITORY} rather
   # than alongside the Makefile.
-  export OUTBASE=${NACL_PACKAGES_REPOSITORY}/${PACKAGE_DIR}
+  export OUTBASE=${SRC_DIR}
   export NACLPORTS_INCLUDE
   export NACLPORTS_PREFIX
   export NACL_PACKAGES_PUBLISH
@@ -38,7 +37,6 @@ BuildStep() {
   fi
   MAKEFLAGS+=" V=1"
   export MAKEFLAGS
-  ChangeDir ${START_DIR}
   DefaultBuildStep
 }
 
@@ -47,6 +45,3 @@ PackageInstall() {
   BuildStep
   InstallStep
 }
-
-PackageInstall
-exit 0