Fortran: Skip bound conv in gfc_conv_gfc_desc_to_cfi_desc with intent(out) ptr [PR108621]

When the dummy argument of the bind(C) proc is 'pointer, intent(out)', the conversion
of the GFC to the CFI bounds can be skipped: it is not needed and avoids issues with
noninit memory.

Note that the 'cfi->base_addr = gfc->addr' assignment is kept as the C code of a user
might assume that a nullified pointer arrives as NULL (or even a specific value).
For instance, gfortran.dg/c-interop/section-{1,2}.f90 assumes the value NULL.

Note 2: The PR is about a may-be-uninitialized warning with intent(out). In the PR's
testcase, the pointer was nullified and should not have produced that warning.
That is a diagnostic issue, now tracked as PR middle-end/108906 as the issue in principle
still exists (e.g. with 'intent(inout)'). [But no longer for intent(out).]

Note 3: With undefined pointers and no 'intent', accessing uninit memory is unavoidable
on the caller side as the compiler cannot know what the C function does (but this usage
determines whether the pointer is permitted be undefined or whether the bounds must be
gfc-to-cfi converted).

gcc/fortran/ChangeLog:

	PR fortran/108621
	* trans-expr.cc (gfc_conv_gfc_desc_to_cfi_desc): Skip setting of
	bounds of CFI desc for 'pointer,intent(out)'.

gcc/testsuite/ChangeLog:

	PR fortran/108621
	* gfortran.dg/c-interop/fc-descriptor-pr108621.f90: New test.