Add top level build script for building packages.

ports/Mesa/build.sh

Index: ports/Mesa/build.sh
diff --git a/ports/Mesa/build.sh b/ports/Mesa/build.sh
old mode 100755
new mode 100644
index 72d0558e25374253a0b507ac4307f570a9b2ee4e..b231e41330bd9de92df32ef34e64e096d705939b
--- a/ports/Mesa/build.sh
+++ b/ports/Mesa/build.sh
@@ -3,8 +3,7 @@
 # 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=${SRC_DIR}
 
 ConfigureStep() {
   # export the nacl tools
@@ -17,7 +16,7 @@ ConfigureStep() {
   export PKG_CONFIG_LIBDIR=${NACLPORTS_PREFIX}/lib
   export PATH=${NACL_BIN_PATH}:${PATH};
   export X11_INCLUDES=
-  ChangeDir ${NACL_PACKAGES_REPOSITORY}/${PACKAGE_NAME}
+  ChangeDir ${BUILD_DIR}
   ./configure \
     --host=nacl \
     --enable-static \
@@ -41,7 +40,3 @@ InstallStep() {
   # assumes pwd has makefile
   make install
 }
-
-
-PackageInstall
-exit 0