CBuilder, link: On Android, always return absolute paths to libraries

Several modules on CPAN expect being able to pass the library
name returned by ->link to DynaLoader::dl_load_file and have it Just Work.
However, because ->link returns relative paths, those modules ran afoul
of Android's linker, which will only look in a handful of hardcoded
system directories for relative libraries, plus whatever LD_LIBRARY_PATH
pointed to at the start of execution.

This commit makes ->link on Android always return an absolute path,
which will be found by the linker.
DynaLoader: On android, dl_load_flags should always be 0x00

The linker ignores all the flags and works as if under RTLD_LOCAL,
so don't give users the headache of seeing warnings ala

	"Can't make loaded symbols global on this platform while loading %s"

when using a module that subclasses DynaLoader and defines
dl_load_flags to anything else.