[PM] Remove the preverifier and directly compute the DominatorTree for
the verifier after ensuring the CFG is at least usefully formed.

This fixes a number of problems:
1) The PreVerifier was missing the controls the Verifier provides over
   *how* an invalid module is handled -- it just aborted the program!
   Now it uses the same logic as the Verifier which is significantly
   more library-friendly.
2) The DominatorTree used previously could have been cached and not
   updated due to bugs in prior passes and we would silently use the
   stale tree. This could cause dominance errors to not be as quickly
   diagnosed.
3) We can now (in the next patch) pull the functionality of the verifier
   apart from the pass infrastructure so that you can verify IR without
   having any form of pass manager. This in turn frees the code to share
   logic between old and new pass manager variants.

Along the way I fixed at least one annoying bug -- the state for
'Broken' wasn't being cleared from run to run causing all functions
visited after the first broken function to be marked as broken
regardless of whether *they* were a problem. Fortunately, I don't really
know much of a way to observe this peculiarity.

In case folks are worried about the runtime cost, its negligible.
I looked at running the entire regression test suite (which should be
a relatively good use of the verifier) before and after but was unable
to even measure the time spent on the verifier and there was no
regresion from before to after. I checked both with debug builds and
optimized builds.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199487 91177308-0d34-0410-b5e6-96231b3b80d8
[asan] extend asan-coverage (still experimental).
 - add a mode for collecting per-block coverage (-asan-coverage=2).
   So far the implementation is naive (all blocks are instrumented),
   the performance overhead on top of asan could be as high as 30%.
 - Make sure the one-time calls to __sanitizer_cov are moved to function buttom,
   which in turn required to copy the original debug info into the call insn.

Here is the performance data on SPEC 2006
(train data, comparing asan with asan-coverage={0,1,2}):

                             asan+cov0     asan+cov1      diff 0-1    asan+cov2       diff 0-2      diff 1-2
       400.perlbench,        65.60,        65.80,         1.00,        76.20,         1.16,         1.16
           401.bzip2,        65.10,        65.50,         1.01,        75.90,         1.17,         1.16
             403.gcc,         1.64,         1.69,         1.03,         2.04,         1.24,         1.21
             429.mcf,        21.90,        22.60,         1.03,        23.20,         1.06,         1.03
           445.gobmk,       166.00,       169.00,         1.02,       205.00,         1.23,         1.21
           456.hmmer,        88.30,        87.90,         1.00,        91.00,         1.03,         1.04
           458.sjeng,       210.00,       222.00,         1.06,       258.00,         1.23,         1.16
      462.libquantum,         1.73,         1.75,         1.01,         2.11,         1.22,         1.21
         464.h264ref,       147.00,       152.00,         1.03,       160.00,         1.09,         1.05
         471.omnetpp,       115.00,       116.00,         1.01,       140.00,         1.22,         1.21
           473.astar,       133.00,       131.00,         0.98,       142.00,         1.07,         1.08
       483.xalancbmk,       118.00,       120.00,         1.02,       154.00,         1.31,         1.28
            433.milc,        19.80,        20.00,         1.01,        20.10,         1.02,         1.01
            444.namd,        16.20,        16.20,         1.00,        17.60,         1.09,         1.09
          447.dealII,        41.80,        42.20,         1.01,        43.50,         1.04,         1.03
          450.soplex,         7.51,         7.82,         1.04,         8.25,         1.10,         1.05
          453.povray,        14.00,        14.40,         1.03,        15.80,         1.13,         1.10
             470.lbm,        33.30,        34.10,         1.02,        34.10,         1.02,         1.00
         482.sphinx3,        12.40,        12.30,         0.99,        13.00,         1.05,         1.06


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199488 91177308-0d34-0410-b5e6-96231b3b80d8
[PM] [cleanup] Rename some of the Verifier's members, re-arrange them,
and tweak comments prior to more invasive surgery. Also clean up some
other non-doxygen comments, and run clang-format over the parts that are
going to change dramatically in subsequent commits so that those don't
get cluttered with formatting changes.

No functionality changed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199489 91177308-0d34-0410-b5e6-96231b3b80d8