[clang] [flang] [flang] Implement -mcmodel flag (PR #95411)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `flang-aarch64-release` running on `linaro-flang-aarch64-release` while building `clang,flang` at step 6 "test-build-unified-tree-check-flang".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/172/builds/636

Here is the relevant piece of the build log for the reference:
```
Step 6 (test-build-unified-tree-check-flang) failure: test (failure)
******************** TEST 'Flang :: Lower/mcmodel.f90' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
RUN: at line 1: /home/tcwg-buildbot/worker/flang-aarch64-release/build/bin/flang-new -fc1 -triple aarch64 -emit-llvm -mcmodel=tiny /home/tcwg-buildbot/worker/flang-aarch64-release/llvm-project/flang/test/Lower/mcmodel.f90 -o - | /home/tcwg-buildbot/worker/flang-aarch64-release/build/bin/FileCheck /home/tcwg-buildbot/worker/flang-aarch64-release/llvm-project/flang/test/Lower/mcmodel.f90 -check-prefix=CHECK-TINY
+ /home/tcwg-buildbot/worker/flang-aarch64-release/build/bin/flang-new -fc1 -triple aarch64 -emit-llvm -mcmodel=tiny /home/tcwg-buildbot/worker/flang-aarch64-release/llvm-project/flang/test/Lower/mcmodel.f90 -o -
+ /home/tcwg-buildbot/worker/flang-aarch64-release/build/bin/FileCheck /home/tcwg-buildbot/worker/flang-aarch64-release/llvm-project/flang/test/Lower/mcmodel.f90 -check-prefix=CHECK-TINY
RUN: at line 2: /home/tcwg-buildbot/worker/flang-aarch64-release/build/bin/flang-new -fc1 -emit-llvm -mcmodel=small /home/tcwg-buildbot/worker/flang-aarch64-release/llvm-project/flang/test/Lower/mcmodel.f90 -o - | /home/tcwg-buildbot/worker/flang-aarch64-release/build/bin/FileCheck /home/tcwg-buildbot/worker/flang-aarch64-release/llvm-project/flang/test/Lower/mcmodel.f90 -check-prefix=CHECK-SMALL
+ /home/tcwg-buildbot/worker/flang-aarch64-release/build/bin/FileCheck /home/tcwg-buildbot/worker/flang-aarch64-release/llvm-project/flang/test/Lower/mcmodel.f90 -check-prefix=CHECK-SMALL
+ /home/tcwg-buildbot/worker/flang-aarch64-release/build/bin/flang-new -fc1 -emit-llvm -mcmodel=small /home/tcwg-buildbot/worker/flang-aarch64-release/llvm-project/flang/test/Lower/mcmodel.f90 -o -
RUN: at line 3: /home/tcwg-buildbot/worker/flang-aarch64-release/build/bin/flang-new -fc1 -triple x86_64-unknown-linux-gnu -emit-llvm -mcmodel=kernel /home/tcwg-buildbot/worker/flang-aarch64-release/llvm-project/flang/test/Lower/mcmodel.f90 -o - | /home/tcwg-buildbot/worker/flang-aarch64-release/build/bin/FileCheck /home/tcwg-buildbot/worker/flang-aarch64-release/llvm-project/flang/test/Lower/mcmodel.f90 -check-prefix=CHECK-KERNEL
+ /home/tcwg-buildbot/worker/flang-aarch64-release/build/bin/FileCheck /home/tcwg-buildbot/worker/flang-aarch64-release/llvm-project/flang/test/Lower/mcmodel.f90 -check-prefix=CHECK-KERNEL
+ /home/tcwg-buildbot/worker/flang-aarch64-release/build/bin/flang-new -fc1 -triple x86_64-unknown-linux-gnu -emit-llvm -mcmodel=kernel /home/tcwg-buildbot/worker/flang-aarch64-release/llvm-project/flang/test/Lower/mcmodel.f90 -o -
error: unable to create target: 'No available targets are compatible with triple "x86_64-unknown-linux-gnu"'
FileCheck error: '<stdin>' is empty.
FileCheck command line:  /home/tcwg-buildbot/worker/flang-aarch64-release/build/bin/FileCheck /home/tcwg-buildbot/worker/flang-aarch64-release/llvm-project/flang/test/Lower/mcmodel.f90 -check-prefix=CHECK-KERNEL

--

********************


```

https://github.com/llvm/llvm-project/pull/95411