Added the TOOL_PREFIX variable for setting up the executable tools.

Currently three different tool chains seem to be used:
   * avr-*
   * pic32-*
   * arm-none-eabi-*

These all get set up independently. This patch centralizes the
definitions of the executable tools and does it generically, by means
of the newly introduced TOOL_PREFIX variable. Setting up a
tool chain is now simply a matter of defining the TOOL_PREFIX
variable. For the currently supported tool chains it gets set to avr,
pic32 or arm-none-eabi. Arbitrary tool chains can now easily be set up,
by the TOOL_PREFIX variable.

Although the use of the OVERRIDE_EXECUTABLES variable is now almost
not justifiable, it was left as-is, in order to assure backwards
compatibility.

0 files changed, 0 insertions, 0 deletions