make llvm-bcanalyzer dump out PCH files symbolically. We should probably

eventually get an option to turn this off, but it is nice for looking at 
statistics.  For example, the types block now prints:

  Block ID #11 (TYPES_BLOCK_ID):
      Num Instances: 1
         Total Size: 895100b/111888B/27971.9W
          % of file: 1.55801
      Num SubBlocks: 0
        Num Abbrevs: 0
        Num Records: 14899
      % Abbrev Recs: 0

        Code Histogram:
                5478    TYPE_FUNCTION_PROTO
                2683    TYPE_TYPEDEF
                2460    TYPE_POINTER
                2047    TYPE_ENUM
                1553    TYPE_RECORD
                283     TYPE_CONSTANT_ARRAY
                274     TYPE_OBJC_INTERFACE
                76      TYPE_INCOMPLETE_ARRAY
                10      TYPE_VECTOR
                9       TYPE_OBJC_QUALIFIED_ID
                5       TYPE_FUNCTION_NO_PROTO
                5       TYPE_EXT_QUAL
                3       TYPE_TYPEOF_EXPR

llvm-svn: 70166