Add .x as XDR/RPCGEN (#3472)

* Add .x as XDR/RPCGEN

XDR/RPC language as documented in RFC5531, RFC4506.
Samples are from glibc and RFCs.

* Add Logos samples

https://github.com/JonasGessner/NoCarrier/blob/master/NoCarrier.x - MIT
cf31f4e466/llvm-gcc-R3/gcc/testsuite/objc/execute/string1.x - GPL2
f6415578fa/perapp-plugin/Tweak.x - GPL3
d1b3e83888/NCHax.x - Apache

* Add disambiguate heuristics for .x

* Add RPC to vendor/README.md

lib/linguist/heuristics.rb

@@ -513,5 +513,13 @@ module Linguist
       end
     end
   
+    disambiguate ".x" do |data|
+      if /\b(program|version)\s+\w+\s*{|\bunion\s+\w+\s+switch\s*\(/.match(data)
+        Language["RPC"]
+      elsif /^%(end|ctor|hook|group)\b/.match(data)
+        Language["Logos"]
+      end
+    end
+
   end
 end

lib/linguist/languages.yml

@@ -3753,6 +3753,17 @@ RMarkdown:
   - ".rmd"
   tm_scope: source.gfm
   language_id: 313
+RPC:
+  type: programming
+  aliases:
+  - rpcgen
+  - oncrpc
+  - xdr
+  ace_mode: c_cpp
+  extensions:
+  - ".x"
+  tm_scope: source.c
+  language_id: 1031374237
 RPM Spec:
   type: data
   tm_scope: source.rpm-spec