Add toolchain cflags that are always used

Some cflags are part of the toolchain selection and should not be
removed by no_default_compiler_flags = true, for example -m32 for x86
compiles.  Removing all the cflags results in hacks such as in crt.mk
where the bare minimum cflags are reinserted.

Add new toolchain interface functions ToolchainCflags, ToolchainLdflags
and ToolchainClangCflags that will always be used.

Change-Id: I0ba02d7611e2afb9ad913319740e00c1bb2d654c
3 files changed