[ClangBuilder] Remove -flang-experimental-exec flag

This flag has been removed from LLVM ( https://reviews.llvm.org/D153379 )

Fix broken bots by also removing the flag here
- clang-aarch64-sve-vla-2stage https://lab.llvm.org/buildbot/#/builders/198/builds/2907
- clang-aarch64-sve-vls-2stage https://lab.llvm.org/buildbot/#/builders/176/builds/2851
- clang-aarch64-sve-vla https://lab.llvm.org/buildbot/#/builders/197/builds/6950
- clang-aarch64-sve-vls https://lab.llvm.org/buildbot/#/builders/184/builds/4485

Reviewed By: awarzynski

Differential Revision: https://reviews.llvm.org/D153501

zorg/buildbot/builders/ClangBuilder.py

@@ -519,7 +519,7 @@ def _getClangCMakeBuildFactory(
                 fortran_flags = [
                         '--cmake-define=TEST_SUITE_FORTRAN:STRING=ON',
                         '--cmake-define=CMAKE_Fortran_FLAGS:STRING=' +
-                            '-flang-experimental-exec -lpgmath',
+                            '-lpgmath',
                         util.Interpolate(
                             '--cmake-define=CMAKE_Fortran_COMPILER=' +
                             '%(prop:builddir)s/'+compiler_path+'/bin/'+fc)]