implement ConfigureOp#check_cxx_compiler

spec/build_tests_spec.rb

@@ -1534,6 +1534,40 @@ EOF
         end
       end
     end
+
+    context "check_cxx_compiler" do
+      {"check_cxx_compiler.rb" => "when no arguments are given",
+       "check_cxx_compiler_find_first.rb" => "when arguments are given"}.each_pair do |rsconsfile, desc|
+        context desc do
+          it "finds the first listed C++ compiler" do
+            test_dir "configure"
+            result = run_rscons(rsconsfile: rsconsfile, op: "configure")
+            expect(result.stderr).to eq ""
+            expect(result.status).to eq 0
+            expect(result.stdout).to match /Checking for C\+\+ compiler\.\.\. g\+\+/
+          end
+
+          it "finds the second listed C++ compiler" do
+            test_dir "configure"
+            create_exe "g++", "exit 1"
+            result = run_rscons(rsconsfile: rsconsfile, op: "configure")
+            expect(result.stderr).to eq ""
+            expect(result.status).to eq 0
+            expect(result.stdout).to match /Checking for C\+\+ compiler\.\.\. clang\+\+/
+          end
+
+          it "fails to configure when it cannot find a C++ compiler" do
+            test_dir "configure"
+            create_exe "g++", "exit 1"
+            create_exe "clang++", "exit 1"
+            result = run_rscons(rsconsfile: rsconsfile, op: "configure")
+            expect(result.stderr).to eq ""
+            expect(result.status).to_not eq 0
+            expect(result.stdout).to match /Checking for C\+\+ compiler\.\.\. not found/
+          end
+        end
+      end
+    end
   end
 
 end