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

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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@36769 91177308-0d34-0410-b5e6-96231b3b80d8