add missing files from 2.1.2 merge

fixes 67c7ce7b79

buildroot/share/PlatformIO/scripts/SAMD21_minitronics20.py

@@ -0,0 +1,19 @@
+#
+# SAMD21_minitronics20.py
+# Customizations for env:SAMD21_minitronics20
+#
+import pioutil
+if pioutil.is_pio_build():
+    from os.path import join, isfile
+    import shutil
+
+    Import("env")
+
+    mf = env["MARLIN_FEATURES"]
+    rxBuf = mf["RX_BUFFER_SIZE"] if "RX_BUFFER_SIZE" in mf else "0"
+    txBuf = mf["TX_BUFFER_SIZE"] if "TX_BUFFER_SIZE" in mf else "0"
+
+    serialBuf = str(max(int(rxBuf), int(txBuf), 350))
+
+    build_flags = env.get('BUILD_FLAGS')
+    env.Replace(BUILD_FLAGS=build_flags)