gnu: abseil-cpp: Update to 20210324.2.

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 <code@greghogan.com>

gnu/packages/cpp.scm

@@ -765,7 +765,8 @@ (define-public tweeny
 point and then, after each tween step, plugging back the result.")
     (license license:expat)))
 
-(define-public abseil-cpp
+;;; This older LTS release is kept for tensorflow.
+(define-public abseil-cpp-20200923.3
   (package
     (name "abseil-cpp")
     (version "20200923.3")
@@ -812,6 +813,26 @@ (define-public abseil-cpp
 Google's C++ code base.")
     (license license:asl2.0)))
 
+(define-public abseil-cpp
+  (let ((base abseil-cpp-20200923.3))
+    (package/inherit base
+      (name "abseil-cpp")
+      (version "20210324.2")
+      (source (origin
+                (method git-fetch)
+                (uri (git-reference
+                      (url "https://github.com/abseil/abseil-cpp")
+                      (commit version)))
+                (file-name (git-file-name name version))
+                (sha256
+                 (base32
+                  "0g9rbhk3mwjdfxk7cscd04vm8fphd5flz9yykpgvyy1nwa34zk3x"))))
+      (arguments
+       (substitute-keyword-arguments (package-arguments base)
+         ((#:configure-flags flags)
+          `(cons* "-DBUILD_TESTING=ON"
+                  (delete "-DABSL_RUN_TESTS=ON" ,flags))))))))
+
 (define-public pegtl
   (package
     (name "pegtl")

gnu/packages/machine-learning.scm

@@ -2211,7 +2211,7 @@ (define-public tensorflow-lite
                       (install-file file target-dir)))
                   (find-files "." "\\.h$")))))))))
     (inputs
-     `(("abseil-cpp" ,abseil-cpp)
+     `(("abseil-cpp" ,abseil-cpp-20200923.3)
        ("eigen" ,eigen-for-tensorflow-lite)
        ("flatbuffers" ,flatbuffers)
        ("python" ,python)))

gnu/packages/rpc.scm

@@ -152,11 +152,13 @@ (define-public grpc-1.16.1
                               "src/core/lib/gpr/log_posix.cc"
                               "src/core/lib/iomgr/ev_epollex_linux.cc")
                  (("gettid\\(")
-                  "sys_gettid("))
-               #t))))))
+                  "sys_gettid("))))))))
     (native-inputs
-     `(("protobuf" ,protobuf-3.6)
-       ,@(alist-delete "protobuf" (package-native-inputs grpc))))))
+     `(("abseil-cpp" ,abseil-cpp-20200923.3)
+       ("protobuf" ,protobuf-3.6)
+       ,@(fold alist-delete (package-native-inputs grpc)
+               '("abseil-cpp"
+                 "protobuf"))))))
 
 (define-public python-grpcio
   (package