Current Toolchain.defs set the compile flags directly, it's OK for
target specified gcc toolchain.
But some LLVM based toolchains (Rust/Zig etc) use single toolchain to handle all supported paltform.
In this patch, arch level Toolchain.defs export standard LLVM style arch flags, and let <Lang>.defs to map them into internal style,
This will simplify the intergration of non-c language.
Signed-off-by: Huang Qi <huangqi3@xiaomi.com>
