gnu: elemental: Update to 0.87.7-0.6eb15a0.

The build of elemental is failed on GCC 7+:
https://github.com/elemental/Elemental/issues/254

Fixed but not released yet in merge request:
https://github.com/elemental/Elemental/pull/259

* gnu/packages/maths.scm (elemental): Update to 0.87.7-0.6eb15a0.

Change-Id: I333f1de160489035f1a8875173abdd57c03ef777
Signed-off-by: Eric Bavier <bavier@posteo.net>

gnu/packages/maths.scm

@@ -7593,18 +7593,23 @@ symmetric matrices.")
     (synopsis "Eigenvalue solvers for symmetric matrices (with MPI support)")))
 
 (define-public elemental
+  ;; The build of 0.87.7 is failed for a long time due to new version of GCC. The
+  ;; latest commit has fixes.
+  ;; See https://github.com/elemental/Elemental/issues/254
+  (let ((commit "6eb15a0da2a4998bf1cf971ae231b78e06d989d9")
+        (revision "0"))
     (package
       (name "elemental")
-    (version "0.87.7")
+      (version (git-version "0.87.7" revision commit))
       (source (origin
                 (method git-fetch)
                 (uri (git-reference
                       (url "https://github.com/elemental/Elemental")
-                     (commit (string-append "v" version))))
+                      (commit commit)))
                 (file-name (git-file-name name version))
                 (sha256
                  (base32
-                "1687xpjjzig27y2pnqv7hv09smpijyfdpz7qjgmcxf4shfajlfkc"))))
+                  "06xcs4ic60ndcf2hq19gr8yjwdsnphpcyhapab41rkw726z4lm7p"))))
       (build-system cmake-build-system)
       (home-page "https://github.com/elemental/Elemental")
       (native-inputs
@@ -7646,7 +7651,7 @@ symmetric matrices.")
       (description "Elemental is a modern C++ library for distributed-memory
 dense and sparse-direct linear algebra, conic optimization, and lattice
 reduction.")
-    (license license:bsd-2)))
+      (license license:bsd-2))))
 
 (define-public mcrl2
   (package