Add -static to static link command, for clang.

Clang driver needs -static flag, not -Bstatic,
to produce statically linked modules.
However, -static is not added if LDFLAGS contains -shared,
which is used in bionic/linker to create a shared object with static libraries.

BUG: 18008984

Change-Id: I75c3e24973ee77170285ec4c8e7aacc345722685