Fortran: fix warnings for symbols with C binding and declared PRIVATE [PR49111]

Fortran: fix warnings for symbols with C binding and declared PRIVATE [PR49111]

The Fortran standard does not prohibit restricting the accessibility of a
symbol by use of the PRIVATE attribute and exposing it via a C binding
label.  Instead of unconditionally generating a warning, only warn if the
binding label is surprisingly identical to the privatized Fortran symbol
and when -Wsurprising is specified.

	PR fortran/49111

gcc/fortran/ChangeLog:

	* decl.cc (verify_bind_c_sym): Modify condition for generation of
	accessibility warning, and adjust warning message.

gcc/testsuite/ChangeLog:

	* gfortran.dg/binding_label_tests_9.f03: Adjust test.
	* gfortran.dg/module_private_2.f90: Likewise.
	* gfortran.dg/public_private_module_2.f90: Likewise.
	* gfortran.dg/binding_label_tests_35.f90: New test.