Add top level build script for building packages.

ports/yajl/build.sh

Index: ports/yajl/build.sh
diff --git a/ports/yajl/build.sh b/ports/yajl/build.sh
old mode 100755
new mode 100644
index caeadb882c274fe8cd83549afbb298800201b96d..de2bea0bd52c188625041ebf9059151f37f57382
--- a/ports/yajl/build.sh
+++ b/ports/yajl/build.sh
@@ -3,20 +3,18 @@
 # 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
 
 TestStep() {
   Banner "Testing ${PACKAGE_NAME}"
   if [ ${NACL_ARCH} == "pnacl" ]; then
     local pexe=test/yajl_test
-    local script=${NACL_BUILD_DIR}/yajl_test.sh
+    local script=${BUILD_DIR}/yajl_test.sh
     TranslateAndWriteSelLdrScript ${pexe} x86-32 ${pexe}.x86-32.nexe ${script}
     (cd ../test && ./run_tests.sh ${script})
     TranslateAndWriteSelLdrScript ${pexe} x86-64 ${pexe}.x86-64.nexe ${script}
     (cd ../test && ./run_tests.sh ${script})
   else
-    local script=${NACL_BUILD_DIR}/yajl_test.sh
+    local script=${BUILD_DIR}/yajl_test.sh
     local nexe=test/yajl_test
 
     WriteSelLdrScript ${script} ${nexe}
@@ -36,7 +34,3 @@ BuildStep() {
   echo "Directory: $(pwd)"
   make all -j${OS_JOBS}
 }
-
-
-PackageInstall
-exit 0