[XRay][compiler-rt] Remove uses of internal allocator in profiling mode

Summary:
This change removes further cases where the profiling mode
implementation relied on dynamic memory allocation. We're using
thread-local aligned (uninitialized) memory instead, which we initialize
appropriately with placement new.

Addresses llvm.org/PR38577.

Reviewers: eizan, kpw

Subscribers: jfb, llvm-commits

Differential Revision: https://reviews.llvm.org/D51278

llvm-svn: 340814