add CFile builder to create C/C++ sources from lex/yacc input files

spec/rscons/builders/cfile_spec.rb

@@ -0,0 +1,23 @@
+module Rscons
+  module Builders
+    describe CFile do
+      let(:env) {Environment.new}
+      subject {CFile.new}
+
+      it "invokes bison to create a .c file from a .y file" do
+        subject.should_receive(:standard_build).with("YACC parser.c", "parser.c", ["bison", "-d", "-o", "parser.c", "parser.y"], ["parser.y"], env, :cache)
+        subject.run("parser.c", ["parser.y"], :cache, env, {})
+      end
+
+      it "invokes a custom lexer to create a .cc file from a .ll file" do
+        env["LEX"] = "custom_lex"
+        subject.should_receive(:standard_build).with("LEX lexer.cc", "lexer.cc", ["custom_lex", "-o", "lexer.cc", "parser.ll"], ["parser.ll"], env, :cache)
+        subject.run("lexer.cc", ["parser.ll"], :cache, env, {})
+      end
+
+      it "raises an error when an unknown source file is specified" do
+        expect {subject.run("file.c", ["foo.bar"], :cache, env, {})}.to raise_error /Unknown source file .foo.bar. for CFile builder/
+      end
+    end
+  end
+end