Annotate No_libcrt with arch_variant

libcrt is crashing libc on x86/x86_64 for unknown reason. This enables
us to disable libcrt for these architectures for libc for now.

Test: m checkbuild
Bug: 29275768
Change-Id: I5a717286b3d9cc1ba8cdcd33bafb9c225de4aff8