Ignore shared libs for static executables.

Ie42edc5184f315f998db953594e425214b810e0e added system_shared_libs to
static libraries so that their exported headers can be referenced.
However, it also added unrequired dependencies, which is an
error-triggering issue for static executables.

This change addresses it by adding a condition to shared libs handling code
in binary.go.

Bug: 121152570
Test: cc_test.go, library_test.go
Change-Id: I1828442c4e496f8d815fccaeca970cd5766bdf5d