create rspec environment for build tests

build_tests/simple/build.rb

@@ -0,0 +1,3 @@
+Rscons::Environment.new do |env|
+  env.Program('simple', Dir['*.c'])
+end

build_tests/simple/simple.c

@@ -0,0 +1,6 @@
+#include <stdio.h>
+
+int main(int argc, char *argv[])
+{
+    printf("This is a simple C program\n");
+}