Add top level build script for building packages.

ports/SDL/build.sh

Index: ports/SDL/build.sh
diff --git a/ports/SDL/build.sh b/ports/SDL/build.sh
old mode 100755
new mode 100644
index ef36b4f47caae59701849bf12d4b590a44e5dd0f..dae07e4aea21e64ff9ad3e5deb313b230e7272ef
--- a/ports/SDL/build.sh
+++ b/ports/SDL/build.sh
@@ -3,8 +3,6 @@
 # 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
 
 AutogenStep() {
   ChangeDir ${NACL_PACKAGES_REPOSITORY}/${PACKAGE_NAME}
@@ -43,9 +41,8 @@ ConfigureTests() {
     conf_host="nacl"
   fi
 
-  ChangeDir ${NACL_PACKAGES_REPOSITORY}/${PACKAGE_NAME}
-  MakeDir ${NACL_BUILD_SUBDIR}-test
-  ChangeDir ${NACL_BUILD_SUBDIR}-test
+  BUILD_DIR=${NACL_PACKAGES_REPOSITORY}/${PACKAGE_NAME}/${NACL_BUILD_SUBDIR}-test
+  ChangeDir ${BUILD_DIR}
 
   LIBS="$LDFLAGS" LogExecute ../test/configure \
     --host=${conf_host} \
@@ -128,7 +125,3 @@ PackageInstall() {
   BuildStep
   PublishStep
 }
-
-
-PackageInstall
-exit 0