boost: fix taxonomy mistake, account taxonomy change in v1.78

This commit makes two changes:

1. Boost changed its taxonomy for architecture names between the 1.77 and
   1.78 releases, in this commit:

   boostorg/context@6edc818

2. During the review of #161162 I [was asked about][1] the source of
   the [mips64-context.patch][2] that I had included in the original
   version of the PR.  I searched through the boost-context revision
   history and found [a nearly identical patch][3], which I
   substituted in the final, merged version of the PR.

   As it turns out, my [mips64-context.patch][2] was an earlier
   revision of what was eventually accepted to boost-context.  The
   only difference between the two patches is the name they use:
   mips64 vs mips1.

   When switching to the accepted version of the boost patch, I should
   have also updated libraries/boost/generic.nix to change mips64 to
   mips1.  This commit does that.

[1]: #161162 (comment)
[2]: https://raw.githubusercontent.com/a-m-joseph/nixpkgs/1ca5025945470ce96408552b9117674b12efaf04/pkgs/development/libraries/boost/mips64-context.patch
[3]: https://github.com/boostorg/context/commit/e3f744a1862164062d579d1972272d67bdaa9c39.patch

pkgs/development/libraries/boost/generic.nix

@@ -84,7 +84,9 @@ let
     # TODO: make this unconditional
   ] ++ optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
     "address-model=${toString stdenv.hostPlatform.parsed.cpu.bits}"
-    "architecture=${if stdenv.hostPlatform.isMips64 then "mips64" else toString stdenv.hostPlatform.parsed.cpu.family}"
+    "architecture=${if stdenv.hostPlatform.isMips64
+                    then if versionOlder version "1.78" then "mips1" else "mips"
+                    else toString stdenv.hostPlatform.parsed.cpu.family}"
     "binary-format=${toString stdenv.hostPlatform.parsed.kernel.execFormat.name}"
     "target-os=${toString stdenv.hostPlatform.parsed.kernel.name}"