makefiles/cflags.inc.mk: don't include absolute path in __FILE__ macro

[benpicco]

Contribution description

__FILE__ will resolve to the absolute path of the file.
This adds a lot of noise (and ROM size) when debugging with tracer macros.

Luckily, starting with GCC 8 we can drop the common $(RIOTBASE) prefix, this makes for much nicer output.

Testing procedure

Used in e.g. #18795

Issues/PRs references

[riot-ci]

Murdock results

✔️ PASSED

5b35910 cpu/esp8266: blacklist -fmacro-prefix-map

Success	Failures	Total	Runtime
117848	0	117848	01h:45m:42s

Artifacts

• Documentation preview

[krzysztof-cabaj]

I use on my old debian arm-none-eabi-gcc version 7.3.1. Addition to OPTIONAL_CFLAG the -fmacro-prefix-map=$(RIOTBASE)/= breaks ability to compile any RIOT program. I receive error:

tests/periph_pwm$ make BOARD=nucleo-l552ze-q
Building application "tests_periph_pwm" for "nucleo-l552ze-q" with MCU "stm32".

arm-none-eabi-gcc: error: unrecognized command line option '-fmacro-prefix-map=/data/RIOT-public/RIOT/='

Is that version of the compiler no longer supported by RIOT?

[benpicco]

Is that version of the compiler no longer supported by RIOT?

Arg, Debian stable ships GCC 8 and the previous Ubuntu LTS GCC 9 so there is a temptation to say yes.

But then again we should just properly detect the compiler version (so we don't penalize users who have a recent avr-gcc just because the Debian package is orphaned).

For now, just add

OPTIONAL_CFLAGS_BLACKLIST += -fmacro-prefix-map=$(RIOTBASE)/=

if you can't update your system.

[krzysztof-cabaj]

Probably adding some if to makefiles which automatically disable this flag for older compilers is wasting a time and only mess makefiles.

I think this is a good time (and reason) to system update.

[benpicco]

Can you try #18935

[krzysztof-cabaj]

PR #18935 works with my old arm-none-eabi-gcc 7.3.1.

Thanks for this PR!

[miri64]

This makes RIOT_FILE_RELATIVE obsolete btw (and since it is also faulty, as it always will use the c-file, even for includes), I guess it can be deprecated and removed now?