Use $(bindir) for path to executable in mkmf

For the macOS -bundle_loader linker option, we need a path to the
Ruby exectuable. $(RUBY) is not necessarily a path since it could
be a command line invocation. That happens during build with
runruby.rb and can happen post installation if the user passes
the --ruby option to a extconf.rb. Use $(bindir) to locate
the executable instead.

Before installation, $(bindir) doesn't exist, so we need to be
able to override $(BUILTRUBY) in such situations so test-spec
and bundled extensions could build. Use a new mkmf global,
$builtruby, to do this; set it in fake.rb and in extmk.rb.

Our build system is quite complex...

1 files changed, 5 insertions, 1 deletions

diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 79bb96ba75..efe3419fd7 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -2076,7 +2076,11 @@ sitearch = #{CONFIG['sitearch']}
 ruby_version = #{RbConfig::CONFIG['ruby_version']}
 ruby = #{$ruby.sub(%r[\A#{Regexp.quote(RbConfig::CONFIG['bindir'])}(?=/|\z)]) {'$(bindir)'}}
 RUBY = $(ruby#{sep})
-BUILTRUBY = $(RUBY)
+BUILTRUBY = #{if defined?($builtruby) && $builtruby
+    $builtruby
+  else
+    File.join('$(bindir)', CONFIG["RUBY_INSTALL_NAME"] + CONFIG['EXEEXT'])
+  end}
 ruby_headers = #{headers.join(' ')}
 
 RM = #{config_string('RM', &possible_command) || '$(RUBY) -run -e rm -- -f'}