Add top level build script for building packages.

ports/git/build.sh

Index: ports/git/build.sh
diff --git a/ports/git/build.sh b/ports/git/build.sh
old mode 100755
new mode 100644
index ac3fad58249ac678726b01c1e58cfeff6b20d133..ef453dd23f8caf6b5c2d0d838989c6bad0d1e8ad
--- a/ports/git/build.sh
+++ b/ports/git/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
 
 # Do a verbose build so we're confident it's hitting nacl's tools.
 export MAKE_TARGETS="V=1"
@@ -16,7 +14,7 @@ ConfigureStep() {
   ChangeDir ${SRC_DIR}
   autoconf
 
-  export NACL_BUILD_DIR=${NACL_PACKAGES_REPOSITORY}/${PACKAGE_DIR}
+  export BUILD_DIR=${NACL_PACKAGES_REPOSITORY}/${PACKAGE_DIR}
   export NACL_CONFIGURE_PATH=./configure
   DefaultConfigureStep
 
@@ -32,6 +30,3 @@ InstallStep() {
   export INSTALL_TARGETS="DESTDIR=${ASSEMBLY_DIR} install"
   DefaultInstallStep
 }
-
-PackageInstall
-exit 0