Added the DIAGNOSTICS_COLOR_WHEN var for controlling diagnostics-color.

Some IDEs do not work nicely with the recently added diagnostics-color
compiler switch. This patch adds the DIAGNOSTICS_COLOR_WHEN variable,
for controlling diagnostics-color switch. The default was chosen to be
'always', which makes the Arduino.mk file backwards compatible with
everything up to commit fa82c3a9db (Sat Sep 2 15:32:52 2017 +0100).

The supported values for DIAGNOSTICS_COLOR_WHEN are: `always`, `never`
and `auto`, and as with all Arduino.mk variables, it can easily be
overridden. For more details on the diagnostics-color compiler switch,
see: https://gcc.gnu.org/onlinedocs/gcc-4.9.2/gcc/Language-Independent-Options.html#Language-Independent-Options

1 files changed, 1 insertions, 0 deletions

diff --git a/HISTORY.md b/HISTORY.md
index 434ed96..12155b4 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -15,6 +15,7 @@ I tried to give credit whenever possible. If I have missed anyone, kindly add it
 - Tweak: Update Windows usage documentation and allow non-relative paths (issue #519) (https://github.com/tuna-f1sh)
 - Tweak: Support Cygwin Unix Python and Windows installation on Windows to pass correct port binding. (https://github.com/tuna-f1sh)
 - New: Added -fdiagnostics-color to \*STD flags (https://github.com/sej7278)
+- New: Made -fdiagnostics-color take a variiable DIAGNOSTICS_COLOR_WHEN: never, always, auto. (https://github.com/wingunder)
 - New: Add generation of tags file using ctags, which automatically includes project libs and Arduino core. (https://github.com/tuna-f1sh)
 - New: Add template Makefile and project boilerplate initialise script, `ardmk-init`. (https://github.com/tuna-f1sh)
 - New: Support atmelice_isp JTAG tool as ISP programmer. (https://github.com/tuna-f1sh)