[MSan] Apply the ctor creation scheme of TSan

Summary: To avoid adding an extern function to the global ctors list, apply the changes of D56538 also to MSan.

Reviewers: chandlerc, vitalybuka, fedor.sergeev, leonardchan

Subscribers: hiraditya, bollu, llvm-commits

Differential Revision: https://reviews.llvm.org/D56734

llvm-svn: 351322