gnu: GSL: Disable failing tests on i686-linux and aarch64-linux.

This follows up commit 7ad3c81240, which enabled
tests that were previously disabled on i686, and takes into account new tests
with similar issues.  While at it, selectively disable tests on aarch64
instead of disabling all tests.

* gnu/packages/maths.scm (gsl)[arguments]: On i686 and aarch64, add #:phases.

gnu/packages/maths.scm

@@ -26,7 +26,7 @@
 ;;; Copyright © 2018 Joshua Sierles, Nextjournal <joshua@nextjournal.com>
 ;;; Copyright © 2018 Nadya Voronova <voronovank@gmail.com>
 ;;; Copyright © 2018 Adam Massmann <massmannak@gmail.com>
-;;; Copyright © 2018 Marius Bakke <mbakke@fastmail.com>
+;;; Copyright © 2018, 2020 Marius Bakke <mbakke@fastmail.com>
 ;;; Copyright © 2018 Eric Brown <brown@fastmail.com>
 ;;; Copyright © 2018 Julien Lepiller <julien@lepiller.eu>
 ;;; Copyright © 2018 Amin Bandali <bandali@gnu.org>
@@ -388,12 +388,35 @@ semiconductors.")
                 "1a460zj9xmbgvcymkdhqh313c4l29mn9cffbi5vf33x3qygk70mp"))))
     (build-system gnu-build-system)
     (arguments
-     `(;; Currently there are numerous tests that fail on "exotic"
+     (let ((system (%current-system)))
-       ;; architectures such as aarch64 and ppc64le.
+       (cond
-       ,@(if (string-prefix? "aarch64-linux"
+        ((string-prefix? "aarch64" system)
-                             (or (%current-target-system) (%current-system)))
+         ;; Some sparse matrix tests are failing on AArch64:
-           '(#:tests? #f)
+         ;; https://lists.gnu.org/archive/html/bug-gsl/2020-04/msg00001.html
-           '())))
+         '(#:phases (modify-phases %standard-phases
+                      (add-before 'check 'disable-failing-tests
+                        (lambda _
+                          (substitute* "spmatrix/test.c"
+                            ((".*test_complex.*") "\n"))
+                          #t)))))
+        ((string-prefix? "i686" (%current-system))
+         ;; There are rounding issues with these tests on i686:
+         ;; https://lists.gnu.org/archive/html/bug-gsl/2016-10/msg00000.html
+         ;; https://lists.gnu.org/archive/html/bug-gsl/2020-04/msg00000.html
+         '(#:phases (modify-phases %standard-phases
+                      (add-before 'check 'disable-failing-tests
+                        (lambda _
+                          (substitute* "linalg/test.c"
+                            ((".*gsl_test\\(test_LU_decomp.*") "\n")
+                            ((".*gsl_test\\(test_LUc_decomp.*") "\n")
+                            ((".*gsl_test\\(test_cholesky_decomp.*") "\n")
+                            ((".*gsl_test\\(test_COD_lssolve2.*") "\n"))
+                          (substitute* "spmatrix/test.c"
+                            ((".*test_all.*") "\n")
+                            ((".*test_float.*") "\n")
+                            ((".*test_complex.*") "\n"))
+                          #t)))))
+        (else '()))))
     (home-page "https://www.gnu.org/software/gsl/")
     (synopsis "Numerical library for C and C++")
     (description