Strip "target:" prefix in solib_find if accessing local files

Strip "target:" prefix in solib_find if accessing local files

This commit updates solib_find to strip the "target:" prefix from
gdb_sysroot when accessing local files.  This ensures that the same
search algorithm is used for local files regardless of whether a
"target:" prefix was used or not.  It also avoids cluttering GDB's
output with unnecessary "target:" prefixes on paths.

gdb/ChangeLog:

	* solib.c (solib_find): Strip "target:" prefix from sysroot
	if accessing local files.