libsigsegv: Remove aarch64 patch, enable tests

The aarch64 patch has been applied upstream. Let's hope that the new
release fixes the tests as well.

pkgs/development/libraries/libsigsegv/aarch64.patch

@@ -1,12 +0,0 @@
-diff --git a/configure b/configure
-index 6c4e868..0298e19 100755
---- a/configure
-+++ b/configure
-@@ -14501,6 +14501,7 @@ else
- 
-     case "$host_cpu" in
-             a29k | \
-+      aarch64* | \
-       alpha* | \
-       arc | \
-       arm* | strongarm* | xscale* | \

pkgs/development/libraries/libsigsegv/default.nix

@@ -8,14 +8,7 @@ stdenv.mkDerivation rec {
     sha256 = "063swdvq7mbmc1clv0rnh20grwln1zfc2qnm0sa1hivcxyr2wz6x";
   };
 
-  # Based on https://github.com/davidgfnet/buildroot-Os/blob/69fe6065b9dd1cb4dcc0a4b554e42cc2e5bd0d60/package/libsigsegv/libsigsegv-0002-fix-aarch64-build.patch
+  doCheck = true;
-  # but applied directly to configure since we can't use autoreconf while bootstrapping.
-  patches = if stdenv.isAarch64 || stdenv.cross.arch or "" == "aarch64"
-    then [ ./aarch64.patch ]
-    else null; # TODO: change to lib.optional on next mass rebuild
-
-  # https://github.com/NixOS/nixpkgs/issues/6028
-  doCheck = false;
 
   meta = {
     homepage = http://www.gnu.org/software/libsigsegv/;