Add top level build script for building packages.

ports/zlib/build.sh

Index: ports/zlib/build.sh
diff --git a/ports/zlib/build.sh b/ports/zlib/build.sh
old mode 100755
new mode 100644
index 757df313da96289e760f779d01b1649dc96fc34b..dcc224628aeb669fd06bbc3a4eee90db230e8ca6
--- a/ports/zlib/build.sh
+++ b/ports/zlib/build.sh
@@ -3,13 +3,13 @@
 # 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
-
+# zlib doesn't support custom build directories so we have
+# to build directly in the source dir.
+BUILD_DIR=${SRC_DIR}
 
 ConfigureStep() {
   Banner "Configuring ${PACKAGE_NAME}"
-  ChangeDir ${NACL_PACKAGES_REPOSITORY}/${PACKAGE_NAME}
+  ChangeDir ${BUILD_DIR}
   LogExecute rm -f libz.*
   # TODO: side-by-side install
   local CONFIGURE_ARGS="--prefix=${NACLPORTS_PREFIX}"
@@ -24,6 +24,7 @@ ConfigureStep() {
   EXECUTABLES="minigzip${NACL_EXEEXT} example${NACL_EXEEXT}"
 }
 
+
 RunMinigzip() {
   export LD_LIBRARY_PATH=.
   if echo "hello world" | ./minigzip | ./minigzip -d; then
@@ -35,6 +36,7 @@ RunMinigzip() {
   unset LD_LIBRARY_PATH
 }
 
+
 RunExample() {
   export LD_LIBRARY_PATH=.
   # This second test does not yet work on nacl (gzopen fails)
@@ -47,6 +49,7 @@ RunExample() {
   unset LD_LIBRARY_PATH
 }
 
+
 TestStep() {
   Banner "Testing ${PACKAGE_NAME}"
   if [ "${NACL_GLIBC}" = "1" ]; then
@@ -93,7 +96,3 @@ PackageInstall() {
     InstallStep
   fi
 }
-
-
-PackageInstall
-exit 0