Revert "BlockGenerator: Generate synthesisable instructions only on-demand"

  This reverts commit 07830c18d789ee72812d5b5b9b4f8ce72ebd4207.

  The commit broke at least one test in lnt,
    MultiSource/Benchmarks/Ptrdist/bc/number.c
  was miss compiled and the test produced a wrong result.

  One Polly test case that was added later was adjusted too.

llvm-svn: 248860