windows-nat: Remove SO_NAME_MAX_PATH_SIZE limit

windows-nat: Remove SO_NAME_MAX_PATH_SIZE limit

There is no need to limit shared library path sizes to
SO_NAME_MAX_PATH_SIZE nowadays.  windows_solib::name and
windows_solib::original_name are std::strings nowadays, and so are
solib::so_name and solib::so_original_name in the core solib code.

This commit reworks the code to remove that limit.  This also fixes a
leak where we were not releasing 'rname' in the realpath branch if the
'rname' string was larger than SO_NAME_MAX_PATH_SIZE.

Note: I tested the cygwin_conv_path with a manual hack to force that
path, and then stepping through the code.  You only get to that path
if Windows doesn't report an absolute path for ntdll.dll, and on my
machine (running Windows 10), it always does.

Approved-By: John Baldwin <jhb@FreeBSD.org>
Change-Id: I79e9862d5a7646eebfef7ab5b05b96318a7ca0c5