Avr-gcc toolchain : Parse CXX/C flags based on build configuration into its proper Avr gcc abstraction layer.

[bebenlebricolo]

This ticket would handle :

• Parsing CMAKE_CXXFLAGS
  • Retrieves flags for each build configuration
  • Provide an abstraction layer of Avr GCC flags and store the compiler flags (aka "Options") in an appropriate data structure
• Makes the distinction between :
  • Optimization flags ("O" options)
  • Debug flags ("-gXX" options)
  • Definitions ("-D=something : preprocessor definitions)
  • Linker options ("-Wl,,...)
  • Global Warning flags ("-Wsomething" options)
  • Regular flags/options ("-fsomething" options)

Note : Most of those options are treated differently by Atmel Studio. Some of them (such as the Optimization ones) get their own specific representation using plain strings, some of them uses "check boxes" within Atmel Studio and are handled differently (e.g. using the "True" value in an Xml node) and finally other ones are just treated as extra flags and do not deserve their own kind of handling.