[compiler-rt] Found one more delta to unbreak build for z/os (PR #82789)

[Rainer Orth via llvm-commits]

rorth wrote:

I've been quite busy with all sorts of issues, including several broken build.

I've now tried this patch on `sparcv9-sun-solaris2.11`, first in a 1-stage build with `gcc-14`, then a 2-stage build also starting from `gcc-14`.  The results weren't good: in both cases I get 3 regressions:
```
  Builtins-sparc-sunos :: compiler_rt_fmaxl_test.c
  Builtins-sparc-sunos :: compiler_rt_logbl_test.c
  Builtins-sparc-sunos :: compiler_rt_scalbnl_test.c
```
The tests fail in the same way:
```
In file included from compiler-rt/test/builtins/Unit/compiler_rt_logbl_test.c:4:
compiler-rt/lib/builtins/fp_lib.h:402:2: error: Unsupported TF mode type
  402 | #error Unsupported TF mode type
      |  ^
```
Even worse, I happened to try a amd64-pc-freebsd14.0 build off the same tree: there the build was broken:
```
AILED: projects/compiler-rt/lib/builtins/CMakeFiles/clang_rt.builtins-i386.dir/extendxftf2.c.o
[...]
In file included from /vol/llvm/src/llvm-project/dist/compiler-rt/lib/builtins/extendxftf2.c:13:
compiler-rt/lib/builtins/fp_lib.h:402:2: error:
Unsupported TF mode type
  402 | #error Unsupported TF mode type
      |  ^
```
This is getting more and more of a nightmare: it feels like completely flying in the dark, (sort of) fixing one port while simultaneously breaking at least two others.  This cannot continue like this without a clear understanding how this is all supposed to work.  It's just an enormous waste of time.

https://github.com/llvm/llvm-project/pull/82789