[clang] [llvm] workflows/release-binaries: Disable flang on Darwin (PR #164667)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-ppc64le-linux-multistage` running on `ppc64le-clang-multistage-test` while building `.github,clang` at step 10 "build stage 2".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/76/builds/13305

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 10 (build stage 2) failure: 'ninja' (failure) (timed out)
...
[6270/6568] Linking CXX executable bin/llvm-dwp
[6271/6568] Linking C executable bin/clang-fuzzer-dictionary
[6272/6568] Linking CXX executable bin/llvm-ir2vec
[6273/6568] Linking CXX executable bin/llvm-c-test
[6274/6568] Linking CXX executable bin/llvm-gsymutil
[6275/6568] Linking CXX executable bin/llvm-libtool-darwin
[6276/6568] Linking CXX executable bin/llvm-dwarfutil
[6277/6568] Linking CXX executable bin/opt
[6278/6568] Building CXX object tools/bugpoint-passes/CMakeFiles/BugpointPasses.dir/TestPasses.cpp.o
[6279/6568] Linking CXX shared module lib/BugpointPasses.so
command timed out: 1200 seconds without output running [b'ninja'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=1705.038306

```

</details>

https://github.com/llvm/llvm-project/pull/164667