Fix build script file copying issue.

build.py

@@ -1,34 +1,44 @@
 import glob
 from subprocess import PIPE, Popen
 from os import listdir, makedirs
-from os.path import join, splitext, isfile
+from os.path import join, splitext
 from shutil import copytree, copy
+from errno import ENOTDIR
 SRC = 'src'
 DST = 'build'
 
 
-def lib_files(s: str):
+def cp(src, dst):
+    try:
+        copytree(src, dst)
+    except OSError as exc:
+        if exc.errno == ENOTDIR:
+            copy(src, dst)
+        else:
+            raise
+
+
+def to_compile(s: str):
     name, ext = splitext(s)
-    if name not in ("code", "boot") and ext == ".py" and isfile(s):
+    if name not in ("code", "boot") and ext == ".py":
         return name
     return None
 
 
 makedirs(DST, exist_ok=True)
+mpy_cross_bin = join(".", glob.glob("mpy-cross.static*")[0])
 
 for entry in listdir(SRC):
     src_path = join(SRC, entry)
-    if name := lib_files(entry):
+    if name := to_compile(entry):
         Popen([
-            join(".", glob.glob("mpy-cross.static*")[0]),
-            src_path, "-o",
-            join(DST, f'{name}.mpy')
+            mpy_cross_bin,
+            "-o",
+            join(DST, f'{name}.mpy'),
+            src_path,
         ],
-            stdout=PIPE
+            stdout=PIPE,
         ).communicate()
     else:
         dst_path = join(DST, entry)
-        if isfile(join(SRC, entry)):
-            copy(src_path, dst_path)
-        else:
-            copytree(src_path, dst_path)
+        cp(src_path, dst_path)