gnu: sbcl: Fix building on armhf-linux.

* gnu/packages/lisp.scm (sbcl)[arguments]: When building for armhf-linux
add a phase to remove build optimizations targeting armv5.

gnu/packages/lisp.scm

@@ -466,6 +466,13 @@ an interpreter, a compiler, a debugger, and much more.")
                   (srfi srfi-1))
        #:phases
        (modify-phases %standard-phases
+         ,@(if (target-arm32?)
+             ;; TODO: Move to snippet in staging.
+             `((add-after 'unpack 'dont-force-armv5
+                 (lambda _
+                   (substitute* "src/runtime/Config.arm-linux"
+                     (("-march=armv5") "")))))
+             '())
          (delete 'configure)
          (add-after 'unpack 'fix-build-id
            ;; One of the build scripts makes a build id using the current date.