Add a test that exercises the abstract base class checking

The test simply tries to instantiate each class exposed as part of the
TOOLCHAIN_CLASSES map. This is a test that each toolchain class
implements the required API, as the mbedToolchain will not allow the
instantiation of a subclass without a part of that API.

Author: theotherjimmy

tools/test/toolchains/api.py

@@ -0,0 +1,13 @@
+import sys
+import os
+
+ROOT = os.path.abspath(os.path.join(os.path.dirname(__file__), "..", "..", ".."))
+sys.path.insert(0, ROOT)
+
+from tools.toolchains import TOOLCHAIN_CLASSES, LEGACY_TOOLCHAIN_NAMES
+from tools.targets import TARGET_MAP
+
+def test_instantiation():
+    for name, Class in  TOOLCHAIN_CLASSES.items():
+        CLS = Class(TARGET_MAP["K64F"])
+        assert name == CLS.name or name ==  LEGACY_TOOLCHAIN_NAMES[CLS.name]