Abstractify the mbedToolchain base class

The mbedToolchain class calls many members of it's subclasses, expecting
them to implement a particular API. This change adds a requirement to
each subclass that requires them to implement this expected API.

The API consists of these methods:
 - parse_dependencies
 - parse_ouptut
 - get_config_option
 - compile_c
 - compile_cpp
 - link
 - archive
 - binary

tools/toolchains/__init__.py

@@ -26,6 +26,7 @@ from os.path import join, splitext, exists, relpath, dirname, basename, split, a
 from inspect import getmro
 from copy import deepcopy
 from tools.config import Config
+from abc import ABCMeta, abstractmethod
 
 from multiprocessing import Pool, cpu_count
 from tools.utils import run_cmd, mkdir, rel_path, ToolException, NotSupportedException, split_path
@@ -230,6 +231,8 @@ class mbedToolchain:
 
     MBED_CONFIG_FILE_NAME="mbed_config.h"
 
+    __metaclass__ = ABCMeta
+
     def __init__(self, target, options=None, notify=None, macros=None, silent=False, extra_verbose=False):
         self.target = target
         self.name = self.__class__.__name__
@@ -784,9 +787,22 @@ class mbedToolchain:
 
         return None
 
+    @abstractmethod
+    def parse_dependencies(self, dep_path):
+        """Take in a dependency file generated by the compiler and build a list of
+           all files that the dep_path depends on.
+        """
+        pass
+
     def is_not_supported_error(self, output):
         return "#error directive: [NOT_SUPPORTED]" in output
 
+    @abstractmethod
+    def parse_output(self, output):
+        """Take in compiler output and extract sinlge line warnings and errors from it
+        """
+        pass
+
     def compile_output(self, output=[]):
         _rc = output[0]
         _stderr = output[1]
@@ -958,6 +974,63 @@ class mbedToolchain:
                 f.write(Config.config_to_header(self.config_data))
         return config_file
 
+    @abstractmethod
+    def get_config_option(self, config_header):
+        """Generate the compiler option that forces the inclusion of the configuration
+        header file.
+        """
+        pass
+
+    @abstractmethod
+    def assemble(self, source, object, includes):
+        """Generate the command line that:
+         - Assembles the given assembly *source* file.
+         - Puts the results into the file named *object*.
+         - Has an include search path that includes everything in *includes*
+        """
+        pass
+
+    @abstractmethod
+    def compile_c(self, source, object, includes):
+        """Generate the command line that:
+         - Compiles the given C *source* file.
+         - Puts the results into the file named *object*.
+         - Has an include search path that includes everything in *includes*
+        """
+        pass
+
+    @abstractmethod
+    def compile_cpp(self, source, object, includes):
+        """Generate the command line that:
+         - Compiles the given C++ *source* file.
+         - Puts the results into the file named *object*.
+         - Has an include search path that includes everything in *includes*
+        """
+        pass
+
+    @abstractmethod
+    def link(self, output, objects, libraries, lib_dirs, mem_map):
+        """Run the link command that will:
+         - Emit a file named *output*
+         - Includes all *objects* and *libraries*
+         - Searches for libraries in *lib_dirs*
+         - Generates a memory map file in the file *mem_map*
+        """
+        pass
+
+    @abstractmethod
+    def archive(self, objects, lib_path):
+        """Run the command line that creates an archive containing *objects*, and named *lib_path*
+        """
+        pass
+
+    @abstractmethod
+    def binary(self, resources, elf, bin):
+        """Run the command line that will Extract a binary named *bin* from an
+        elf file named *elf*.
+        """
+        pass
+
     # Return the list of macros geenrated by the build system
     def get_config_macros(self):
         return Config.config_to_macros(self.config_data) if self.config_data else []