[Fortran/gfortran] Use -O0 for cshift_bounds_[34]. (#191)

* [Fortran/gfortran] Use -O0 for cshift_bounds_[34].

There is no support for `-fbounds-check` in Flang yet.
There is a related feature request at https://github.com/orgs/llvm/projects/12?pane=issue&itemId=29048733
Until then, the optimizations may replace the Fortran runtime calls
(which usually provide all the error checking) with inline sequences
that do not check for errors to provide the fast code
(e.g. llvm/llvm-project#119480).
For the time being I would like to explicitly pass `-O0`
to these tests.

* Disabled tests.

* Reverted tests.cmake

Author: vzakhari

Fortran/gfortran/regression/DisabledFiles.cmake

@@ -1642,6 +1642,12 @@ file(GLOB FAILING_FILES CONFIGURE_DEPENDS
   maxloc_bounds_5.f90
   ptr_func_assign_1.f08
 
+  # Tests looking for runtime errors (e.g., bound checks). Correctly
+  # caught by flang runtime, but not caught with Flang optimizations,
+  # e.g. due to intrinsics inlining. These can pass with -O0:
+  cshift_bounds_3.f90
+  cshift_bounds_4.f90
+
   # Bad test, assigning an 11 elements array to a 12 elements array.
   transfer_array_intrinsic_4.f90