Add an option that allows one to "decode" the LSDA.

Add an option that allows one to "decode" the LSDA.

The LSDA is a bit difficult for the non-initiated to read. Even with comments,
it's not always clear what's going on. This wraps the ASM streamer in a class
that retains the LSDA and then emits a human-readable description of what's
going on in it.

So instead of having to make sense of:

Lexception1:
        .byte   255
        .byte   155
        .byte   168
        .space  1
        .byte   3
        .byte   26
Lset0 = Ltmp7-Leh_func_begin1
      .long     Lset0
Lset1 = Ltmp812-Ltmp7
      .long     Lset1
Lset2 = Ltmp913-Leh_func_begin1
      .long     Lset2
      .byte     3
Lset3 = Ltmp812-Leh_func_begin1
      .long     Lset3
Lset4 = Leh_func_end1-Ltmp812
      .long     Lset4
      .long     0
      .byte     0
      .byte     1
      .byte     0
      .byte     2
      .byte     125
      .long     __ZTIi@GOTPCREL+4
      .long     __ZTIPKc@GOTPCREL+4

you can read this instead:

## Exception Handling Table: Lexception1
##  @LPStart Encoding: omit
##    @TType Encoding: indirect pcrel sdata4
##        @TType Base: 40 bytes
## @CallSite Encoding: udata4
## @Action Table Size: 26 bytes

## Action 1:
##   A throw between Ltmp7 and Ltmp812 jumps to Ltmp913 on an exception.
##     For type(s):  __ZTIi@GOTPCREL+4 __ZTIPKc@GOTPCREL+4
## Action 2:
##   A throw between Ltmp812 and Leh_func_end1 does not have a landing pad.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@133286 91177308-0d34-0410-b5e6-96231b3b80d8