[SPARC] Revamp AnalyzeBranch and add ReverseBranchCondition.

[SPARC] Revamp AnalyzeBranch and add ReverseBranchCondition.

AnalyzeBranch on X86 (and, previously, SPARC, which implementation was
copied from X86) tries to modify the branches based on block
layout (e.g. checking isLayoutSuccessor), when AllowModify is true.

The rest of the architectures leave that up to the caller, which can
call InsertBranch, RemoveBranch, and ReverseBranchCondition as
appropriate. That appears to be the preferred way to do it nowadays.

This commit makes SPARC like the rest: replaces AnalyzeBranch with an
implementation cribbed from AArch64, and adds a ReverseBranchCondition
implementation.

Additionally, a test-case has been added (also cribbed from AArch64)
demonstrating that redundant branch sequences no longer get emitted.

E.g., it used to emit code like this:
         bne .LBB1_2
         nop
         ba .LBB1_1
         nop
 .LBB1_2:

And now emits:
        cmp %i0, 42
        be .LBB1_1
        nop

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@257572 91177308-0d34-0410-b5e6-96231b3b80d8