Split up source and added basic support for different targets.

targets/_any/SConscript

@@ -0,0 +1,17 @@
+Import('env')
+
+any_target_sources = Split('''
+    src/app/main.cpp
+
+    src/os/panic.cpp
+    src/os/tty.cpp
+
+    src/cstdlib/assert.cpp
+    src/cstdlib/stdio.cpp
+    src/cstdlib/stdlib.cpp
+    src/cstdlib/string.cpp
+''')
+
+env.Append(KERNEL_SOURCES = [env.File(f) for f in any_target_sources])
+
+Return('env')