Fix building static host executables.

BUILD_HOST_static=1 forces all host binaries to be statically linked.
Since -nodefaultlibs was passed (to disable libstdc++), libgcc wasn't
being passed. This change emulates the driver's behavior.

Also fix default STL selection for BUILD_HOST_static.

Bug: 19567451
Change-Id: I617aab782d40ac76ca5a7d9dddf0f202a4e3a69b