Tested the same way as I did #10008:

As far as I can tell (and checked with colordiff -u <(git show | grep "^-" | sed 's/^-//g') <(git show | grep "^+" | sed 's/^+//g')) this just moves and ifdefs some code around. After a local rebase to include #9981 I also was able to build this with tests/periph_gpio both with periph_gpio_irq manually added or removed to FEATURES_OPTIONAL. Without periph_gpio_irq the binary is significantly smaller with this PR than in master.

I used arduino-due as a board for the compile tests.

As with #9997, this PR needed another level of diffing, because the move wasn't that obvious, but I checked this as well:

colordiff -u \
    <(diff -u <(git show | grep "^-" | sed 's/^-//g') \
              <(git show | grep "^+" | sed 's/^+//g') | grep "^-" | sed 's/^-//g') \
    <(diff -u <(git show | grep "^-" | sed 's/^-//g') \
              <(git show | grep "^+" | sed 's/^+//g') | grep "^+" | sed 's/^+//g')