PR 50892 Latent bug in char pointer assignment

PR 50892 Latent bug in char pointer assignment

Due to r256284 (PR 78534) there was a latent bug that reared it's head
due to different character length types in the pointer
assignment. Fixed by this patch, which also adds a reduced testcase.

Regtested on x86_64-pc-linux-gnu, committed to trunk as obvious.

gcc/fortran/ChangeLog:

2018-01-06  Janne Blomqvist  <jb@gcc.gnu.org>

	PR fortran/50892
	* trans-expr.c (gfc_trans_pointer_assignment): fold_convert rhs to
	lhs type.

gcc/testsuite/ChangeLog:

2018-01-06  Janne Blomqvist  <jb@gcc.gnu.org>

	PR fortran/50892
	* gfortran.dg/char_pointer_assign_icb_1.f90: New test.

From-SVN: r256310