Honor the 'SOURCE_DATE_EPOCH' environment variable to allow for
determinitic builds.

--- a/Lib/py_compile.py
+++ b/Lib/py_compile.py
@@ -105,7 +105,10 @@ def compile(file, cfile=None, dfile=None, doraise=False):
     """
     with open(file, 'U') as f:
         try:
-            timestamp = long(os.fstat(f.fileno()).st_mtime)
+            if 'SOURCE_DATE_EPOCH' in os.environ:
+                timestamp = long(os.environ['SOURCE_DATE_EPOCH'])
+            else:
+                timestamp = long(os.fstat(f.fileno()).st_mtime)
         except AttributeError:
             timestamp = long(os.stat(file).st_mtime)
         codestring = f.read()
diff --git a/Python/import.c b/Python/import.c
index e47ce63..7eecf9c 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -945,6 +945,11 @@ write_compiled_module(PyCodeObject *co, char *cpathname, struct stat *srcstat, t
     /* Now write the true mtime (as a 32-bit field) */
     fseek(fp, 4L, 0);
     assert(mtime <= 0xFFFFFFFF);
+    if (Py_GETENV("SOURCE_DATE_EPOCH") != NULL) {
+	const char *epoch = Py_GETENV("SOURCE_DATE_EPOCH");
+	mtime = atoi(epoch);
+    }
+
     PyMarshal_WriteLongToFile((long)mtime, fp, Py_MARSHAL_VERSION);
     fflush(fp);
     fclose(fp);
e/gnu/packages/rpc.scm?id=c5e436b0b1a4d2d8637f8f08e662619f3f7fe881'>tree</a><a href='/guix/commit/gnu/packages/rpc.scm?id=c5e436b0b1a4d2d8637f8f08e662619f3f7fe881'>commit</a><a href='/guix/diff/gnu/packages/rpc.scm?id=c5e436b0b1a4d2d8637f8f08e662619f3f7fe881'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/packages/rpc.scm'>
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<div class='path'>path: <a href='/guix/log/?id=c5e436b0b1a4d2d8637f8f08e662619f3f7fe881'>root</a>/<a href='/guix/log/gnu?id=c5e436b0b1a4d2d8637f8f08e662619f3f7fe881'>gnu</a>/<a href='/guix/log/gnu/packages?id=c5e436b0b1a4d2d8637f8f08e662619f3f7fe881'>packages</a>/<a href='/guix/log/gnu/packages/rpc.scm?id=c5e436b0b1a4d2d8637f8f08e662619f3f7fe881'>rpc.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/rpc.scm?id=c5e436b0b1a4d2d8637f8f08e662619f3f7fe881&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-12-13 17:48:25 +0100'>2021-12-13</span></td><td><a href='/guix/commit/gnu/packages/rpc.scm?id=8394619baceb118df92e355377fd543bb1aa501a'>gnu: Simplify package inputs.</a><span class='msg-avail'>...<span class='msg-tooltip'>This commit was obtained by running:

  ./pre-inst-env guix style

without any additional argument.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-11-11 10:31:25 -0500'>2021-11-11</span></td><td><a href='/guix/commit/gnu/packages/rpc.scm?id=f0ce5a6051e6071178eb01f2c9be66a123f56096'>gnu: abseil-cpp: Update to 20210324.2.</a><span class='msg-avail'>...<span class='msg-tooltip'>But keep the older variant for Tensorflow.

* gnu/packages/cpp.scm (abseil-cpp-20200923.3): Renamed older variant.
(abseil-cpp): New variable.
* gnu/packages/machine-learning.scm (tensorflow-lite)
[inputs]: Adjust to use the older abseil-cpp-20200923.3.
* gnu/packages/rpc.scm (grpc-1.16.1)[native-inputs]: Likewise.

Co-authored-by: Greg Hogan &lt;code@greghogan.com&gt;
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-07-04 14:42:30 +0300'>2021-07-04</span></td><td><a href='/guix/commit/gnu/packages/rpc.scm?id=73a5891d744c69ab01433b568ba5c55dd927f139'>gnu: grpc-1.16.1: Build with older protobuf.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/rpc.scm (grpc-1.16.1)[native-inputs]: Replace protobuf
with protobuf-3.6.
</span></span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2021-06-25 00:39:38 +0200'>2021-06-25</span></td><td><a href='/guix/commit/gnu/packages/rpc.scm?id=88beddccead0f502d0434bd818b3fa33ce0a6fe2'>gnu: apache-thrift: Update to 0.14.2.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/rpc.scm (apache-thrift): Update to 0.14.2.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>