Skip this performance regression test.

The test measures things on the order of 20ms.  On a loaded machine, we
have seen enough variation that the test would fail.

--- grep-2.22/tests/long-pattern-perf	2016-01-03 12:52:38.491575007 +0100
+++ grep-2.22/tests/long-pattern-perf	2016-01-03 12:53:39.768464687 +0100
@@ -16,6 +16,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+exit 77
 . "${srcdir=.}/init.sh"; path_prepend_ ../src
 
 fail=0
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<tr><td><span title='2019-02-28 19:15:02 +0100'>2019-02-28</span></td><td><a href='/guix/commit/gnu/packages/groff.scm?id=b4037d82c0d30455ca9288e18a543dbb310476ac'>gnu: groff: Return #t from all phases.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/groff.scm (groff)[arguments]: Return #t from phases.
</span></span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2019-02-28 19:13:54 +0100'>2019-02-28</span></td><td><a href='/guix/commit/gnu/packages/groff.scm?id=5466e82a1e61349e5a3f9726a03874e4f9817226'>gnu: groff: Adjust relocatability snippet for 1.22.4.</a><span class='msg-avail'>...<span class='msg-tooltip'>This commit does three things.  It reverts 73b2ce87 ("gnu: groff-minimal:
Disable relocatability."), re-applies f57693e1 ("gnu: groff: Disable
relocatability."), and finally adjusts the substitution for changes since
0559a4c2 ("gnu: groff: Update to 1.22.4.").

* gnu/packages/groff.scm (groff-minimal)[arguments]: Move relocatibility
snippet ...
(groff)[arguments]: ... here.  Don't delete relocation.cpp and adjust file name.
</span></span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2019-02-06 13:03:26 +0100'>2019-02-06</span></td><td><a href='/guix/commit/gnu/packages/groff.scm?id=ba88eea2b3a8a33ecd7fc0ec64e3917c6c2fe21d'>Merge branch 'master' into core-updates</a></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2019-01-17 10:07:07 +0100'>2019-01-17</span></td><td><a href='/guix/commit/gnu/packages/groff.scm?id=73b2ce87956b0d9168dcfa234128b91e0e41a4c7'>gnu: groff-minimal: Disable relocatability.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/groff.scm (groff-minimal)[arguments]&lt;#:phases&gt;
[disable-relocatability]: New phase.
</span></span></td><td>Danny Milosavljevic</td></tr>
<tr><td><span title='2019-01-16 18:31:27 +0200'>2019-01-16</span></td><td><a href='/guix/commit/gnu/packages/groff.scm?id=96733e941754759d4a1f45ef8fb05dc9ff6db7b3'>Revert "gnu: groff: Disable relocatability."</a><span class='msg-avail'>...<span class='msg-tooltip'>This causes more than 3600 packages to be rebuilt.

This reverts commit f57693e17c7905d2f11e46d04cb558fe0b0fc39b.
</span></span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2019-01-16 15:15:30 +0100'>2019-01-16</span></td><td><a href='/guix/commit/gnu/packages/groff.scm?id=f57693e17c7905d2f11e46d04cb558fe0b0fc39b'>gnu: groff: Disable relocatability.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/groff.scm (groff)[arguments]&lt;#:phases&gt;[disable-relocatability]:
New phase.
</span></span></td><td>Danny Milosavljevic</td></tr>
<tr><td><span title='2019-01-14 15:34:54 -0600'>2019-01-14</span></td><td><a href='/guix/commit/gnu/packages/groff.scm?id=2df4f7020d2c49110900f786af7700d170c3035c'>gnu: groff: Fix doc installation.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/groff.scm (groff)[arguments]: Add 'fix-docdir phase.
</span></span></td><td>Eric Bavier</td></tr>
<tr><td><span title='2019-01-07 11:59:04 +0200'>2019-01-07</span></td><td><a href='/guix/commit/gnu/packages/groff.scm?id=0559a4c2ca5b2573d5086c8b64794a634fc3e799'>gnu: groff: Update to 1.22.4.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/groff.scm (groff): Update to 1.22.4.
[source]: Remove patch.
(groff-minimal)[arguments]: Update configure flags to skip documentation.
* gnu/packages/patches/groff-source-date-epoch.patch: Remove file.
* gnu/local.mk (dist_patch_DATA): Remove it.
</span></span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2018-05-06 15:47:20 +0200'>2018-05-06</span></td><td><a href='/guix/commit/gnu/packages/groff.scm?id=06fc895f29735d6cae482522ba433165611b55c1'>gnu: groff-minimal: Preserve 'preconv' executable.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/groff.scm (groff-minimal)[arguments]: Add 'preconv' to the list
of kept programs.
</span></span></td><td>Marius Bakke</td></tr>