Add detection for the XC programming language.

lib/linguist/languages.yml

@@ -1222,6 +1222,13 @@ Visual Basic:
   - .vba
   - .vbs
 
+XC:
+  type: programming
+  lexer: C
+  primary_extension: .xc
+  extensions:
+  - .xc
+
 XML:
   type: markup
   ace_mode: xml

samples/XC/main.xc

@@ -0,0 +1,10 @@
+int main()
+{
+  int x;
+  chan c;
+  par {
+    c <: 0;
+    c :> x;
+  }
+  return x;
+}