[ASan] Enable build with ASan.

[ASan] Enable build with ASan.

This patch enables ASan instrumentation for glibc.

1. Modifies rltd to support calling init for libasan.so
before libc.so. Also changes don't brake backward
compatibility against libpthread.so, because rtld will add
libpthread.so as a first library to initlist.

2. Changes the type of symbol __sched_cpucount from IFUNC
to FUNC, to avoid segfault at the relocation stage.
IFUCN is a spectial type of symbol which allows to call
resolver at the relocation stage (symbol binding),
so resolver instrumented with ASan will cause a segfault.

Change-Id: I99b6e230605801123e3e132f9934c75fae4e6cfa