Switch to GCC v10.3 for Arduino core

Resolves #301, resolves #486, resolves #605, resolves #650

Author: valeros

platform.json

@@ -77,7 +77,8 @@
       "optionalVersions": [
         "~1.60301.0",
         "~1.80201.0",
-        "~1.90201.0"
+        "~1.90201.0",
+        "~1.100301.0"
       ]
     },
     "framework-mbed": {

platform.py

@@ -47,7 +47,7 @@ def configure_default_packages(self, variables, targets):
                 self.packages["framework-arduinoststm32l0"]["optional"] = False
                 self.packages["framework-arduinoststm32"]["optional"] = True
             else:
-                self.packages["toolchain-gccarmnoneeabi"]["version"] = "~1.90201.0"
+                self.packages["toolchain-gccarmnoneeabi"]["version"] = "~1.100301.0"
                 self.packages["framework-cmsis"]["version"] = "~2.50700.0"
                 self.packages["framework-cmsis"]["optional"] = False