Create TARGET_GLOBAL_CLANGPP_FLAGS & filter-out CLANG_CONFIG_UNKNOWN_CFLAGS
from TARGET_GLOBAL_CPPFLAGS. Prior to this, if a unknown CLANG_FLAG was in
TARGET_GLOBAL_CPPFLAGS you would get a clang++ error.

Plus reduce space wasted by indirect duplicate rules:
ifneq ($(TARGET_CLANG_VERSION),)
ifeq ($(LOCAL_CLANG),true)

&&

ifeq ($(TARGET_CLANG_VERSION),)
ifeq ($(LOCAL_CLANG),true)

Change-Id: I38ae521882537df4cc4627fe1ca7145e7dc9a31b
MY GOTO & LDFLAGS

Change-Id: I3ed147f180267db975ee556a4730c2c1dad2d554