compiler-rt: Consolidate and fix cmake arguments

compiler-rt: Consolidate and fix cmake arguments

Specify CMAKE_C_COMPILER_TARGET and COMPILER_RT_DEFAULT_TARGET_ARCH
in common for native/target/nativesdk

set COMPILER_RT_DEFAULT_TARGET_ARCH to use HOST_ARCH across all recipe
variants

It is not needed to set COMPILER_RT_DEFAULT_TARGET_ARCH for powerpc anymore
as it is already fixed by setting COMPILER_RT_DEFAULT_TARGET_ARCH to
HOST_ARCH

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>