tests/extmod: Add platform_basic.py for basic coverage test of platform.

Signed-off-by: Jeff Epler <jepler@gmail.com>

tests/extmod/platform_basic.py

@@ -0,0 +1,8 @@
+try:
+    import platform
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+print(type(platform.python_compiler()))
+print(type(platform.libc_ver()))