patch pr100067-revert references non-existent file "arm.c"

[Markus Ueberall]

When trying to rebuild gcc-12 using pbuilder, the following error pops up:

Applying patch pr100067-revert.diff
can't find file to patch at input line 5
Perhaps you used the wrong -p or --strip option?
The text leading up to this was:
--------------------------
|# DP: Revert the fix for PR target/100067, breaking the ARM multilib build
|
|--- a/src/gcc/config/arm/arm.c
|+++ b/src/gcc/config/arm/arm.c
--------------------------
No file to patch. Skipping patch.
3 out of 3 hunks ignored

There's only a file .../arm.cc, so this might be a typo. How this could have been packaged and tested is beyond me, though.