[compiler-rt][asan][hwasan] Fix Fuchsia build

Fix build failure in Fuchsia build from refactoring in
5d2be1a1

Guard the moved versions of ReserveShadowMemoryRange and ProtectGap
the same way they were in the asan code originally (not for Fuchsia or
RTEMS). Otherwise we end up with unsats as they invoke functions not
defined there.