New ld.so argument --inhibit-ldcache to disable ld.so.cache lookup

New ld.so argument --inhibit-ldcache to disable ld.so.cache lookup

It may sometimes be desirable to make the dynamic linker only pick up
libraries from the library path and rpath and not look at the
ld.so.cache that ldconfig generates. An example of such a use case is
the glibc testsuite where the dynamic linker must not be influenced by
any external paths or caches.

This change adds a new option --inhibit-ldcache that when used, tells
the dynamic linker to not use ld.so.cache even if it is available.