[GlobalISel] Check if branches use the same MBB in matchOptBrCondByInvertingCond

[ornata]

If the G_BR + G_BRCOND in this combine use the same MBB, then it will infinite
loop. Don't allow that to happen.

Differential Revision: https://reviews.llvm.org/D95895

(cherry picked from commit 02d4b36)

rdar://73842004

[ornata]

@swift-ci please test

[ornata]

Test failures on Linux platform are all unrelated to this commit:

Failed Tests (10):
  Clangd :: background-index.test
  Clangd :: check-fail.test
  Clangd :: check.test
  Clangd :: compile-commands-path-in-initialize.test
  Clangd :: path-mappings.test
  Clangd :: system-include-extractor.test
  Clangd :: target_info.test
  Clangd Unit Tests :: ./ClangdTests/DirectoryBasedGlobalCompilationDatabaseCacheTest.Cacheable
  Clangd Unit Tests :: ./ClangdTests/GlobalCompilationDatabaseTest.BuildDir
  Clangd Unit Tests :: ./ClangdTests/GlobalCompilationDatabaseTest.DiscoveryWithNestedCDBs

This is safe to merge.