Drop use of the deprecated time.clock which was removed in Python 3.8.

Adapted from upstream pull request:

https://github.com/dlitz/pycrypto/pull/296

diff --git a/lib/Crypto/Random/_UserFriendlyRNG.py b/lib/Crypto/Random/_UserFriendlyRNG.py
--- a/lib/Crypto/Random/_UserFriendlyRNG.py
+++ b/lib/Crypto/Random/_UserFriendlyRNG.py
@@ -73,8 +73,11 @@ class _EntropyCollector(object):
         t = time.time()
         self._time_es.feed(struct.pack("@I", int(2**30 * (t - floor(t)))))
 
-        # Add the fractional part of time.clock()
-        t = time.clock()
+        # Add the fractional part of time.process_time()
+        try:
+           t = time.process_time()
+        except AttributeError:
+           t = time.clock()
         self._clock_es.feed(struct.pack("@I", int(2**30 * (t - floor(t)))))
 
 
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<tr><td><span title='2020-08-11 16:25:06 +0200'>2020-08-11</span></td><td><a href='/guix/commit/gnu/packages/musl.scm?id=ec291843ce89081775a30c063c65e7a20abb2270'>gnu: musl: Update to 1.2.1.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/musl.scm (musl): Update to 1.2.1.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-02-26 21:52:48 +0100'>2020-02-26</span></td><td><a href='/guix/commit/gnu/packages/musl.scm?id=233332c2e9cb76927dd7573b24bd7cdf7afca993'>gnu: musl: Update to 1.2.0.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/musl (musl): Update to 1.2.0.

Signed-off-by: Marius Bakke &lt;mbakke@fastmail.com&gt;
</span></span></td><td>Vincent Legoll</td></tr>