add an abbreviation for the type symtab, this shrinks the TST from 175197 bits

to 103165 bits:

Old:
  Block ID #13 (TYPE_SYMTAB):
      Num Instances: 1
         Total Size: 175197b/21899.6B/5474.91W
       Average Size: 175197b/21899.6B/5474.91W
          % of file: 0.657023
  Tot/Avg SubBlocks: 0/0
    Tot/Avg Abbrevs: 0/0
    Tot/Avg Records: 255/255
      % Abbrev Recs: 0

New:
  Block ID #13 (TYPE_SYMTAB):
      Num Instances: 1
         Total Size: 103165b/12895.6B/3223.91W
       Average Size: 103165b/12895.6B/3223.91W
          % of file: 0.387937
  Tot/Avg SubBlocks: 0/0
    Tot/Avg Abbrevs: 1/1
    Tot/Avg Records: 255/255
      % Abbrev Recs: 100

llvm-svn: 36769