Add -Wl,--exclude-libs=libclang_rt.builtins to ldflags

libclang_rt.builtins has default visiblity set to public and is the
last included static library for all modules.  This means that it is
possible for libraries to pick up libclang_rt.builtins from their
shared library dependencies, instead of libclang_rt.builtins directly.

Particularly, a vendor prebuilt in AOSP was picking up __floatditf()
from libhidlbase.so instead of from libclang_rt.builtins.  A change to
libhidlbase.so that removed the symbol caused thos prebuilt to fail to
link at runtime.

Bug: 138809247
Test: build, boot internal
Test: don't see libclang_rt.builtins symbols in libhidlbase.so

Merged-In: I0348c4860fe02cf88cb89f7ab356bd8c17826d77
Change-Id: I0348c4860fe02cf88cb89f7ab356bd8c17826d77