[esan] Initialize runtime during early interceptors
Adds initialization of esan's runtime library during any early interceptors
that are sometimes called prior to the official __esan_init() invocation
(we see this with apps using tcmalloc).
Adds handling of interceptors called during interceptor initialization.
Subscribers: vitalybuka, zhaoqin, kcc, eugenis, llvm-commits, kubabrecka
Differential Revision: http://reviews.llvm.org/D20976