- adds a "namespace" for each header
- makes clear where a header is expected to come from
- better facilitates explicit includes

ver 5.7+ of the CMSIS library (arm_math / DSP) defines these exact same
symbols as "intrinsics" (the ASM is the same), and since CMSIS headers
and imxrt.h are included at some points (e.g. Audio library code) this
needs to be resolved