Remove libcpp_is_static

This change makes libc++ a shared_library iff is_component_build=true, just like
all other components.  This has the advantage that the RPATH doesn't need to be
set in sanitizer (non-component) builds just so binaries can find libc++.so.

Needed for src CL:
https://chromium-review.googlesource.com/c/chromium/src/+/1119098

R=thakis
BUG=850682

Change-Id: Iaaa5a0426bac852e5ffd6768ece813f31b8f299f
3 files changed