[Bug target/91135] [9/10 Regression] __linux__ not defined with -mcall-aixdesc on 9.x and ppc64

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91135

--- Comment #8 from Segher Boessenkool <segher at gcc dot gnu.org> ---
-mcall-* should change the calling convention, not anything else OS-related.

-mcall-aixdesc is the *default* for powerpc64-linux.