[stack-safety] Local analysis implementation

Summary:
Analysis produces StackSafetyInfo which contains information with how allocas
and parameters were used in functions.

From prototype by Evgenii Stepanov and  Vlad Tsyrklevich.

Reviewers: eugenis, vlad.tsyrklevich, pcc, glider

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D54504

llvm-svn: 347603