Optimize byte-aligned copies in copy_bitwise()

Optimize byte-aligned copies in copy_bitwise()

The function copy_bitwise used for copying DWARF pieces can potentially
be invoked for large chunks of data.  For instance, consider a large
struct one of whose members is currently located in a register.  In this
case copy_bitwise would still copy the data bitwise in a loop, which is
much slower than necessary.

This change uses memcpy for the large part instead, if possible.

gdb/ChangeLog:

	* dwarf2loc.c (copy_bitwise): Use memcpy for the middle part, if
	it is byte-aligned.