[BOLT] Add an option to specialize memcpy() for 1 byte copy

Summary:
Add an option:

  -memcpy1-spec=func1,func2:cs1,func3:cs1:cs2,...

to specialize calls to memcpy() in listed functions (the name could be
supplied in regex) for size 1. The optimization will dynamically check
if the size argument equals to 1 and execute a one byte copy, otherwise
it will call memcpy() as usual. Specific call sites could be indicated
after ":" using their numeric count from the start of the function.

(cherry picked from FBD15428936)