Merge pull request #2463 from Shopify/Alex/cpp-compat

Enable `-Wc++-compat`

Author: soutaro

ext/rbs_extension/extconf.rb

@@ -11,7 +11,13 @@
 $srcs = Dir.glob("#{root_dir}/src/**/*.c") +
         Dir.glob("#{root_dir}/ext/rbs_extension/*.c")
 
-append_cflags ['-std=gnu99', '-Wimplicit-fallthrough', '-Wunused-result']
+append_cflags [
+  '-std=gnu99',
+  '-Wimplicit-fallthrough',
+  '-Wunused-result',
+  '-Wc++-compat',
+]
+
 append_cflags ['-O0', '-g'] if ENV['DEBUG']
 if ENV["TEST_NO_C23"]
   puts "Adding -Wc2x-extensions to CFLAGS"