Merge #21065: build: make macOS HOST in download-osx generic

f22a3ec build: make macOS HOST in download-osx generic (fanquake)

Pull request description:

  This was missed in #20419, and the update before that, so just make this non-versioned so that we don't have to worry about it. This is fine, because it's just for downloading sources.

ACKs for top commit:
  RandyMcMillan:
    ACK f22a3ec
  dongcarl:
    utACK f22a3ec

Tree-SHA512: 3a6993a69594a793a5185e4ba48858443a1002a37b96ff881d39ca7719c79432b35d709bd9a9379f8046bdbeb716c5e1598f273a7e7e3f3bf528b6a807abe5ec

Author: fanquake

depends/Makefile

@@ -265,7 +265,7 @@ install: check-packages $(host_prefix)/share/config.site
 download-one: check-sources $(all_sources)
 
 download-osx:
-	@$(MAKE) -s HOST=x86_64-apple-darwin14 download-one
+	@$(MAKE) -s HOST=x86_64-apple-darwin download-one
 download-linux:
 	@$(MAKE) -s HOST=x86_64-unknown-linux-gnu download-one
 download-win: