[builtins] Build for arm64e for Darwin

[smeenai]

Summary

https://github.com/apple/swift/pull/30112/ makes the Swift standard
library for iOS build for arm64e. If you're building Swift against your
own LLVM, this in turn requires having the builtins built for arm64e,
otherwise you won't be able to use the builtins (which will in turn lead
to an undefined symbol for __isOSVersionAtLeast). Make the builtins
build for arm64e to fix this.

[rjmccall]

Seems reasonable.

compiler-rt/cmake/builtin-config-ix.cmake

 set(RISCV32 riscv32)
 set(RISCV64 riscv64)
 set(SPARC sparc)
 set(SPARCV9 sparcv9)
 set(WASM32 wasm32)
 set(WASM64 wasm64)
 
 if(APPLE)
-  set(ARM64 arm64)
+  set(ARM64 arm64 arm64e)
   set(ARM32 armv7 armv7k armv7s)
   set(X86_64 x86_64 x86_64h)
 endif()
 
 set(ALL_BUILTIN_SUPPORTED_ARCH ${X86} ${X86_64} ${ARM32} ${ARM64}
     ${HEXAGON} ${MIPS32} ${MIPS64} ${PPC64} ${RISCV32} ${RISCV64} ${SPARC} ${SPARCV9} ${WASM32} ${WASM64})
 
 include(CompilerRTUtils)

compiler-rt/lib/builtins/CMakeLists.txt

if (MINGW)
   )
 endif()
 
 set(armhf_SOURCES ${arm_SOURCES})
 set(armv7_SOURCES ${arm_SOURCES})
 set(armv7s_SOURCES ${arm_SOURCES})
 set(armv7k_SOURCES ${arm_SOURCES})
 set(arm64_SOURCES ${aarch64_SOURCES})
+set(arm64e_SOURCES ${aarch64_SOURCES})
 
 # macho_embedded archs
 set(armv6m_SOURCES ${thumb1_SOURCES})
 set(armv7m_SOURCES ${arm_SOURCES})
 set(armv7em_SOURCES ${arm_SOURCES})
 
 # hexagon arch
 set(hexagon_SOURCES