Place object files next to source files for source files in build directory - close #171

build_tests/simple/build_root_source_path.rb

@@ -0,0 +1,13 @@
+env("e", echo: :command) do |env|
+  source_file = "#{env.build_root}/src/foo.c"
+  FileUtils.mkdir_p(File.dirname(source_file))
+  File.open(source_file, "w") do |fh|
+    fh.puts(<<-EOF)
+    int main()
+    {
+      return 29;
+    }
+    EOF
+  end
+  env.Program("foo.exe", source_file)
+end