make -print-stats print stats about the amount of the SLoc

make -print-stats print stats about the amount of the SLoc
address space we used up.  Some interesting data:

For c99-intconst-1.c:
6912762 SLocEntry's allocated, 25592386B of Sloc address space used.

For cocoa.h:
26469 SLocEntry's allocated, 10278752B of Sloc address space used.

For carbon.h:
27364 SLocEntry's allocated, 12398141B of Sloc address space used.

Clearly 2G of sloc address space should be enough for anyone?!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@63093 91177308-0d34-0410-b5e6-96231b3b80d8