Fix resolution on non-musl platforms

Gems without specific platform were being preferred over matching
platform specific gems.

Author: deivid-rodriguez

lib/rubygems/resolver.rb

@@ -246,7 +246,7 @@ def search_for(dependency)
 
     sources.each do |source|
       groups[source].
-        sort_by {|spec| [spec.version, Gem::Platform.local =~ spec.platform ? 1 : 0] }.
+        sort_by {|spec| [spec.version, spec.platform =~ Gem::Platform.local ? 1 : 0] }.
         map {|spec| ActivationRequest.new spec, dependency }.
         each {|activation_request| activation_requests << activation_request }
     end

test/rubygems/test_gem_resolver.rb

@@ -391,6 +391,39 @@ def test_does_not_pick_musl_variants_on_non_musl_linux
     end
   end
 
+  def test_pick_generic_linux_variants_on_musl_linux
+    util_set_arch "aarch64-linux-musl" do
+      is = Gem::Resolver::IndexSpecification
+
+      linux = Gem::Platform.new("aarch64-linux")
+
+      spec_fetcher do |fetcher|
+        fetcher.spec "libv8-node", "15.14.0.1" do |s|
+          s.platform = linux
+        end
+
+        fetcher.spec "libv8-node", "15.14.0.1"
+      end
+
+      v15 = v("15.14.0.1")
+      source = Gem::Source.new @gem_repo
+
+      s = set
+
+      v15_ruby = is.new s, "libv8-node", v15, source, Gem::Platform::RUBY
+      v15_linux = is.new s, "libv8-node", v15, source, linux.to_s
+
+      s.add v15_linux
+      s.add v15_ruby
+
+      ad = make_dep "libv8-node", "= 15.14.0.1"
+
+      res = Gem::Resolver.new([ad], s)
+
+      assert_resolves_to [v15_linux.spec], res
+    end
+  end
+
   def test_only_returns_spec_once
     a1 = util_spec "a", "1", "c" => "= 1"
     b1 = util_spec "b", "1", "c" => "= 1"