Fortran: Emit correct types for CHARACTER(C_CHAR), VALUE arguments

Make the front-end emit the right type for CHARACTER(C_CHAR), VALUE
arguments to BIND(C) procedures. They are scalar integers of C type
char, and should be emitted as such. They are not strings or arrays,
and are not promoted to C int, either.

gcc/fortran/ChangeLog:

	PR fortran/103828
	* trans-decl.c (generate_local_decl): Do not call
	gfc_conv_scalar_char_value(), but check the type tree.
	* trans-expr.c (gfc_conv_scalar_char_value): Rename to
	conv_scalar_char_value, do not alter type tree.
	(gfc_conv_procedure_call): Adjust call to renamed
	conv_scalar_char_value() function.
	* trans-types.c (gfc_sym_type): Take care of
	CHARACTER(C_CHAR), VALUE arguments.
	* trans.h (gfc_conv_scalar_char_value): Remove prototype.

gcc/testsuite/ChangeLog:

	PR fortran/103828
	* gfortran.dg/c_char_tests_3.f90: New file.
	* gfortran.dg/c_char_tests_3_c.c: New file.
	* gfortran.dg/c_char_tests_4.f90: New file.
	* gfortran.dg/c_char_tests_5.f90: New file.