The current version of code uses isARM to check if we are compiling to any arm target then checks the target bit width to either add the 32-bit sources or 64-bit source.  However, isARM only returns true for 32-bit targets, and isAARCH64 is for the 64-bit targets.

I also replaced the unreachable with a @panic when we receive an unsupported arch because this code is reachable and should turn into an error.