Add missing include statement for compatibility with libstdc++ 11.

Taken from upstream:

  https://github.com/llvm/llvm-project/commit/b498303066a63a203d24f739b2d2e0e56dca70d1

diff --git a/utils/benchmark/src/benchmark_register.h b/utils/benchmark/src/benchmark_register.h
--- a/utils/benchmark/src/benchmark_register.h
+++ b/utils/benchmark/src/benchmark_register.h
@@ -1,6 +1,7 @@
 #ifndef BENCHMARK_REGISTER_H
 #define BENCHMARK_REGISTER_H
 
+#include <limits>
 #include <vector>
 
 #include "check.h"
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<tr><td><span title='2020-07-25 13:55:57 +0200'>2020-07-25</span></td><td><a href='/guix/commit/gnu/packages/smalltalk.scm?id=30d6eb85dac539e19994f4637dfc60ecf8826c0b'>gnu: squeak-vm: Enter build directory once.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/smalltalk.scm (squeak-vm)[arguments]: Use CHDIR instead of
pseudofunctional WITH-DIRECTORY-EXCURSIONs.  Drop the custom ‘build’ phase.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-07-25 13:55:56 +0200'>2020-07-25</span></td><td><a href='/guix/commit/gnu/packages/smalltalk.scm?id=b3c1dac11b108252491f88c0a2d8a4bde7575b9d'>gnu: squeak-vm: Update home page.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/smalltalk.scm (squeak-vm)[source, home-page]: Drop ‘www’ subdomain.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>