The existing ARCH Makefile variable is exported to the C code as well.
Additionally the version (arm-only for now) is detected as well. This
allows to for complete autodetection, i.e. that optimized ASM is picked up
if determined by preprocessor (CPU_ARM, etc).
Building a sim/raaa on a arm host will now automatically generate a arm
optmized build like we have for native targets.
Change-Id: I0b35393f8fb3ebd20beaa9e7371fa57bf3782107
Example: for a file asm/foo.c, make will look for asm/arm/foo.[cS] and
compile it if found. If not found it'll fall back to asm/foo.c.
Also introduce new ARCH make variable. This is automatically detected by
configure. It is distinct from CPU since CPU defines the dir used for
the target tree (i.e. firmware/target/X, so it can be "hosted").
ARCH really has the target isa and can be x86 for sims/raaa too.
Change-Id: I18e5d2b7b7bbc2ad2be551a74a0fcae5ffbcbf8b
