PR modula2/118600 Assigning to a record causes alignment exception

PR modula2/118600 Assigning to a record causes alignment exception

This patch recursively tests every assignment (of a constructor
to a designator) to ensure the types are GCC equivalent.  If they
are equivalent then it uses gimple assignment and if not then it
copies a structure by field and uses __builtin_strncpy to copy a
string cst into an array.  Unions are copied by __builtin_memcpy.

gcc/m2/ChangeLog:

	PR modula2/118600
	* gm2-compiler/M2GenGCC.mod (PerformCodeBecomes): New procedure.
	(CodeBecomes): Refactor and call PerformCodeBecomes.
	* gm2-gcc/m2builtins.cc (gm2_strncpy_node): New global variable.
	(DoBuiltinStrNCopy): New function.
	(m2builtins_BuiltinStrNCopy): New function.
	(m2builtins_init): Initialize gm2_strncpy_node.
	* gm2-gcc/m2builtins.def (BuiltinStrNCopy): New procedure
	function.
	* gm2-gcc/m2builtins.h (m2builtins_BuiltinStrNCopy): New
	function.
	* gm2-gcc/m2statement.cc (copy_record_fields): New function.
	(copy_array): Ditto.
	(copy_strncpy): Ditto.
	(copy_memcpy): Ditto.
	(CopyByField_Lower): Ditto.
	(m2statement_CopyByField): Ditto.
	* gm2-gcc/m2statement.def (CopyByField): New procedure function.
	* gm2-gcc/m2statement.h (m2statement_CopyByField): New function.
	* gm2-gcc/m2type.cc (check_record_fields): Ditto.
	(check_array_types): Ditto.
	(m2type_IsGccStrictTypeEquivalent): Ditto.
	* gm2-gcc/m2type.def (IsGccStrictTypeEquivalent): New procedure
	function.
	* gm2-gcc/m2type.h (m2type_IsAddress): Replace return type int
	with bool.

Signed-off-by: Gaius Mulley <gaiusmod2@gmail.com>