InitializeInterceptors() calls dlsym(), which calls calloc(). Depending
on the allocator implementation, calloc() may invoke mmap(), which
results in a segfault since REAL(mmap) is still being resolved.
We fix this by doing a direct syscall if interceptors haven't been fully
resolved yet.
Reviewed By: vitalybuka
Differential Revision: https://reviews.llvm.org/D86168