gfortran: Fix allocation of diagnostig string (was too small).

gfortran: Fix allocation of diagnostig string (was too small).

The attached patch fixes an out of bound write to memory allocated
with alloca() on the stack.  This rarely ever happened because on
one hand -fbounds-check needs to be enabled, and on the other hand
alloca() used to allocate a few bytes extra most of the time so
most of the time the excess write did no harm.

gcc/fortran/ChangeLog:

	* trans-array.c (gfc_conv_array_ref): Fix allocation of diagnostic
	message (was too small).

From-SVN: r238849