fortran: Unshare associate var charlen [PR104228]

fortran: Unshare associate var charlen [PR104228]

PR104228 showed that character lengths were shared between associate
variable and associate targets.  This is problematic when the associate
target is itself a variable and gets a variable to hold the length, as
the length variable is added (and all the variables following it in the chain)
to both the associate variable scope and the target variable scope.
This caused an ICE when compiling with -O0 -fsanitize=address.

This change forces the creation of a separate character length for the
associate variable.  It also forces the initialization of the character
length variable to avoid regressing associate_32 and associate_47 tests.

	PR fortran/104228

gcc/fortran/ChangeLog:

	* resolve.cc (resolve_assoc_var): Also create a new character
	length for non-dummy associate targets.
	* trans-stmt.cc (trans_associate_var): Initialize character length
	even if no temporary is used for the associate variable.

gcc/testsuite/ChangeLog:

	* gfortran.dg/asan/associate_58.f90: New test.
	* gfortran.dg/asan/associate_59.f90: New test.