Privatizer: transform @malloc and global variables to allocaInst

[chenxiao2402]

Add src/tools/privatizer and it will do the following optimization in each hot function:

• Transform callInsts to @malloc into allocaInst.
• Transform uses of global variables into uses of allocaInst.

These optimizations will only be triggered when privatizer ensures they will not change output of the program, or cause segment fault.