ardupilotwaf: add -fno-math-errno to ChibiOS boards

Allows better use of math instructions as opposed to calling library
functions to implement math like `sqrt`. This saves flash and increases
speed. ArduPilot does not use EDOM or ERANGE anyway.

Might cause issues with malloc errno:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88576 but ArduPilot does
not check for ENOMEM or use errno much anyway.

Tools/ardupilotwaf/boards.py

@@ -1165,6 +1165,7 @@ def configure_env(self, cfg, env):
             '-fno-builtin-vprintf',
             '-fno-builtin-vfprintf',
             '-fno-builtin-puts',
+            '-fno-math-errno',
             '-mno-thumb-interwork',
             '-mthumb',
             '--specs=nano.specs',