[rubygems/rubygems] Fix resolution hanging on musl platforms

After recent musl support was added, Bundler started hanging in musl
platforms. I identified the issue where valid candidates were being
filtered out because their platform was specified as a string, and thus
`Gem::Platform.match_spec?` which under the hood ends up calling
`Gem::Platform#===` would return `nil`, because it does not support
comparing platforms to strings.

In particular, `Bundler::EndpointSpecification`'s platform coming from
the API was not instantiated as a `Gem::Platform`, hence the issue.

Also, this spec surfaced another issue where a bug corrected in
`Gem::Platform#match_platforms` had not been yet backported to Bundler.
So this commit also backports that to get the spec green across RubyGems
versions.

Finally, the fix in `Bundler::EndpointSpecification` made a realworld
spec start failing. This spec was faking out `rails-4.2.7.1` requirement
on Bundler in the `Gemfile.lock` file to be `>= 1.17, < 3` when the real
requirement is `>= 1.17, < 2`. Due to the bug in
`Bundler::EndpointSpecification`, the real requirement provided by the
compact index API (recorded with VCR) was being ignored, and the
`Gemfile.lock` fake requirement was being used, which made the spec
pass. This is all expected, and to fix the issue I changed the spec to
be really realworld and don't fake any Bundler requirements.

https://github.com/rubygems/rubygems/commit/faf4ef46bc

1 files changed, 17 insertions, 0 deletions

diff --git a/spec/bundler/runtime/platform_spec.rb b/spec/bundler/runtime/platform_spec.rb
index 84c8dfcab3..caf69bf085 100644
--- a/spec/bundler/runtime/platform_spec.rb
+++ b/spec/bundler/runtime/platform_spec.rb
@@ -344,6 +344,23 @@ RSpec.describe "Bundler.setup with multi platform stuff" do
     expect(the_bundle).to include_gems "platform_specific 1.0 RUBY"
   end
 
+  it "pulls platform specific gems correctly on musl" do
+    build_repo4 do
+      build_gem "nokogiri", "1.13.8" do |s|
+        s.platform = "aarch64-linux"
+      end
+    end
+
+    simulate_platform "aarch64-linux-musl" do
+      install_gemfile <<-G, :artifice => "compact_index", :env => { "BUNDLER_SPEC_GEM_REPO" => gem_repo4.to_s }, :verbose => true
+        source "https://gems.repo4"
+        gem "nokogiri"
+      G
+    end
+
+    expect(out).to include("Fetching nokogiri 1.13.8 (aarch64-linux)")
+  end
+
   it "allows specifying only-ruby-platform on windows with dependency platforms" do
     simulate_windows do
       install_gemfile <<-G