Build LLVM with -Wno-deprecated-declarations

The external/llvm and frameworks/compile/mclinker repositories aren't
being updated with upstream source, so it makes sense to ignore
deprecation warnings. There are ~3000 warnings from std::unary_function
and std::binary_function after upgrading libc++.

Also: replace -std=c++11 cppflag with Soong's cpp_std property.

Bug: http://b/333165689
Test: treehugger, build with topic:use-prebuilt-libcxx
Change-Id: Iffc4d15340980baff51ef56a3aba80514cb1ac88
1 file changed