Repository: spack/spack

Issue:
subversion build error
```spack install subversion``` on Centos 7 produced this error

``` bash
config.status: executing svn_private_config.h.tmp commands
==> 'make'
cd subversion/libsvn_subr && /bin/sh "/tmp/spack-stage/spack-stage-uEDL_Z/subversion-1.9.5/libtool" --tag=CC --silent --mode=link spack/lib/spack/env/gcc/gcc  -g -O2  -g -O2 -pthread   -Lspack/opt/spack/linux-centos7-x86_64/gcc-4.8.5/serf-1.3.8-hykdq2iyglzduqjliagtt3xurt7aliyf/lib     -rpath spack/opt/spack/linux-centos7-x86_64/gcc-4.8.5/subversion-1.9.5-su23sjmdgfw5kztzd6ly46djwmg4sc4n/lib -version-info 0 -Wl,--no-undefined -o libsvn_subr-1.la  adler32.lo atomic.lo auth.lo base64.lo bit_array.lo cache-inprocess.lo cache-membuffer.lo cache-memcache.lo cache.lo cache_config.lo checksum.lo cmdline.lo compat.lo compress.lo config.lo config_auth.lo config_file.lo config_win.lo crypto.lo ctype.lo date.lo debug.lo deprecated.lo dirent_uri.lo dso.lo eol.lo error.lo fnv1a.lo gpg_agent.lo hash.lo io.lo iter.lo lock.lo log.lo macos_keychain.lo magic.lo md5.lo mergeinfo.lo mutex.lo nls.lo object_pool.lo opt.lo packed_data.lo path.lo pool.lo prefix_string.lo prompt.lo properties.lo quoprint.lo root_pools.lo simple_providers.lo skel.lo sorts.lo spillbuf.lo sqlite.lo sqlite3wrapper.lo ssl_client_cert_providers.lo ssl_client_cert_pw_providers.lo ssl_server_trust_providers.lo stream.lo string.lo subst.lo sysinfo.lo target.lo temp_serializer.lo time.lo token.lo types.lo user.lo username_providers.lo utf.lo utf8proc.lo utf_validate.lo utf_width.lo validate.lo version.lo win32_crashrpt.lo win32_crypto.lo win32_xlate.lo x509info.lo x509parse.lo xml.lo -Lspack/opt/spack/linux-centos7-x86_64/gcc-4.8.5/apr-util-1.5.4-frfa4hqtc6sxdog7u73l5ce4osbfw4ov/lib -laprutil-1 -Lspack/opt/spack/linux-centos7-x86_64/gcc-4.8.5/apr-1.5.2-jjeu2n3zxjasxhytyn3yn4vgji37oqci/lib -lapr-1 -lexpat -Lspack/opt/spack/linux-centos7-x86_64/gcc-4.8.5/zlib-1.2.11-yrijbmajetpxrkyaa4uclsyw62zbhc5m/lib -lz  -Lspack/opt/spack/linux-centos7-x86_64/gcc-4.8.5/sqlite-3.8.5-mzsollqygzja7txlau5xo5lzodmewnv7/lib -lsqlite3
.libs/xml.o: In function `expat_entity_declaration':
/tmp/spack-stage/spack-stage-uEDL_Z/subversion-1.9.5/subversion/libsvn_subr/xml.c:386: undefined reference to `XML_StopParser'
collect2: error: ld returned 1 exit status
make: *** [subversion/libsvn_subr/libsvn_subr-1.la] Error 1
```

Subversion fails because its build system does not check that apr-utils was compiled with expat

Adding the following to apr-util fixed the subversion build
``` bash 
depends_on('expat')

```

``` bash
options.append('--with-expat=%s' % spec['expat'].prefix)
```


Discussion:
Feel free to contribute a PR!
Just a minute!

Resolving patch:
diff --git a/var/spack/repos/builtin/packages/apr-util/package.py b/var/spack/repos/builtin/packages/apr-util/package.py
--- a/var/spack/repos/builtin/packages/apr-util/package.py
+++ b/var/spack/repos/builtin/packages/apr-util/package.py
@@ -33,12 +33,14 @@ class AprUtil(Package):
     version('1.5.4',    '866825c04da827c6e5f53daff5569f42')
 
     depends_on('apr')
+    depends_on('expat')
 
     def install(self, spec, prefix):
 
         # configure, build, install:
         options = ['--prefix=%s' % prefix]
         options.append('--with-apr=%s' % spec['apr'].prefix)
+        options.append('--with-expat=%s' % spec['expat'].prefix)
 
         configure(*options)
         make()


Test patch: