Revert to non-parallel build for subversion.

ports/subversion/build.sh

 # Copyright (c) 2014 The Native Client Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+# subversion's build system seem to have a bug with out-of-tree builds
+# and parallel building that was causing occational flakes on the buildbots.
+# The mkdir-init target appears to be required before any object file can be
+# built but none of the object files seem to depend on this.
+OS_JOBS=1
+
 NACLPORTS_CPPFLAGS+=" -Dmain=nacl_main"
 
 export LIBS+=" -Wl,--undefined=nacl_main ${NACL_CLI_MAIN_LIB} -lppapi_simple \
   -lnacl_io -lppapi -lppapi_cpp -l${NACL_CPP_LIB}"
 
 EXTRA_CONFIGURE_ARGS="--with-apr=${NACL_PREFIX}"
 EXTRA_CONFIGURE_ARGS+=" --with-apr-util=${NACL_PREFIX}"
 EXTRA_CONFIGURE_ARGS+=" --enable-all-static"
 
 if [ "${NACL_LIBC}" = "newlib" ]; then
   NACLPORTS_CPPFLAGS+=" -I${NACLPORTS_INCLUDE}/glibc-compat"
   export LIBS+=" -lglibc-compat"
 fi
 
 InstallStep() {
   PublishByArchForDevEnv
 }