sanitizers: Do not include crypt.h if SANITIZER_INTERCEPT_CRYPT_R is undef

sanitizer_intercept_overriders.h might override SANITIZER_INTERCEPT_CRYPT_R to
be undefined. There's no need to require crypt.h in that case.

(The motivation is that crypt() moved from glibc into its own package at some
point, which makes intercepting it and building with a single sysroot that
supports both pre-bullseye and post-bullseye a bit hairy.)

Differential Revision: https://reviews.llvm.org/D126696