Add "GCC Machine Description" language.

lib/linguist/heuristics.rb

@@ -239,6 +239,14 @@ module Linguist
       end
     end
 
+    disambiguate ".md" do |data|
+      if /^[-a-z0-9=#!\*\[|]/i.match(data)
+        Language["Markdown"]
+      elsif /^(;;|\(define_)/.match(data)
+        Language["GCC machine description"]
+      end
+    end
+
     disambiguate ".ml" do |data|
       if /(^\s*module)|let rec |match\s+(\S+\s)+with/.match(data)
         Language["OCaml"]

lib/linguist/languages.yml

@@ -1182,6 +1182,13 @@ GAS:
   tm_scope: source.assembly
   ace_mode: assembly_x86
 
+GCC Machine Description:
+  type: programming
+  extensions:
+  - .md
+  tm_scope: source.lisp
+  ace_mode: lisp
+
 GDScript:
   type: programming
   extensions: