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='2022-12-18 01:16:47 +0100'>2022-12-18</span></td><td><a href='/guix/commit/nix/libutil/util.cc?id=2d4d26769d6a3be1b21302b0bb2bd099fd55ccf8'>daemon: Make "opening file" error messages distinguishable.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-11-19 23:04:19 +0100'>2021-11-19</span></td><td><a href='/guix/commit/nix/libutil/util.cc?id=24224530d1f4a70808d003ba8dce849b77625b79'>daemon: Micro-optimize 'deletePath'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-12-08 22:30:07 +0100'>2020-12-08</span></td><td><a href='/guix/commit/nix/libutil/util.cc?id=2e308238ad09e9527f9b8c3ec4a90b6b05a93367'>daemon: 'Agent' constructor takes a list of environment variables.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-09-14 15:42:55 +0200'>2020-09-14</span></td><td><a href='/guix/commit/nix/libutil/util.cc?id=ee9dff34f9317509cb2b833d07a0d5e01a36a4ae'>daemon: Move 'Agent' to libutil.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-03-26 12:59:33 +0100'>2020-03-26</span></td><td><a href='/guix/commit/nix/libutil/util.cc?id=d0ed201e0a9736c64cb3c59d8c987c79fd6046d6'>daemon: Avoid kill -1 bug on the Hurd.</a><span class='msg-avail'>...</span></td><td>Manolis Ragkousis</td></tr>
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