$ bin/spack install mpich%clang 
==> Installing mpich
==> Using cached archive: /Users/harrison37/Work/alpine/spack/var/spack/cache/mpich/mpich-3.2.1.tar.gz
==> Staging archive: /Users/harrison37/Work/alpine/spack/var/spack/stage/mpich-3.2.1-gmk64r7kkptknk4e2knl7zlof6tqirfo/mpich-3.2.1.tar.gz
==> Created stage in /Users/harrison37/Work/alpine/spack/var/spack/stage/mpich-3.2.1-gmk64r7kkptknk4e2knl7zlof6tqirfo
1 out of 1 hunk FAILED -- saving rejects to file src/include/mpiimpl.h.rej
==> Patch mpich32_clang.patch failed.
==> Error: ProcessError: Command exited with status 1:
    '/usr/bin/patch' '-s' '-p' '1' '-i' '/Users/harrison37/Work/alpine/spack/var/spack/repos/builtin/packages/mpich/mpich32_clang.patch' '-d' '.'
==> Error: [Errno 2] No such file or directory: '/Users/harrison37/Work/alpine/spack/var/spack/stage/mpich-3.2.1-gmk64r7kkptknk4e2knl7zlof6tqirfo/mpich-3.2.1/spack-build.out'...

bin/spack install mpich@3.2%clang
==> Installing mpich
==> Fetching http://www.mpich.org/static/downloads/3.2/mpich-3.2.tar.gz
######################################################################## 100.0%
==> Staging archive: /Users/harrison37/Work/alpine/spack/var/spack/stage/mpich-3.2-gea6brxmwnhbxy5xsj6xzp454jbgguta/mpich-3.2.tar.gz
==> Created stage in /Users/harrison37/Work/alpine/spack/var/spack/stage/mpich-3.2-gea6brxmwnhbxy5xsj6xzp454jbgguta
==> Applied patch mpich32_clang.patch
==> Building mpich [AutotoolsPackage]
==> Executing phase: 'autoreconf'
==> Executing phase: 'configure'