bmake: restore missing bsd.*.mk symlinks on Darwin

bmake's installPhase was updated in #462500 to manually install the
binaries and share Makefiles for bmake as the boot-strap script invokes
bmake (breaking cross builds). This caused the darwin.locale build to
regress as bmake could no longer find bsd.prog.mk [1]. The install-sh
script (which is invoked by the install-mk target used by the boot-strap
script) creates bsd.-prefixed symlinks to the Makefiles under share on
BSD systems, including Darwin. Update bmake's installPhase to invoke
install-mk to ensure that the symlinks are created. install-mk does not
invoke bmake so this should not break cross builds.

[1]: https://github.com/apple-oss-distributions/adv_cmds/blob/2bdd0b49a2d51a3249eecdb04277da034f54eca6/locale/BSDmakefile#L9

pkgs/by-name/bm/bmake/package.nix

@@ -96,8 +96,8 @@ stdenv.mkDerivation (finalAttrs: {
     # `boot-strap op=install` runs the built bmake, which breaks cross builds.
     install -Dm755 bmake $out/bin/bmake
     install -Dm644 bmake.1 $man/share/man/man1/bmake.1
-    mkdir -p $out/share
-    cp -r mk $out/share
+    install -Dm755 -d $out/share/mk
+    sh mk/install-mk -v -m 444 $out/share/mk
 
     runHook postInstall
   '';