[RC1] Status of Mingw MSYS

Good evening, guys!

I suppose mingw build would be stable, though, I would like some
patches to be picked up.

* RC1

LLVM and clang can be built on either msys/autoconf, msys/cmake and mingw/cmake.
By CMake, all tests can run but 37 of LLVM and 5 of clang tests would fail.
On mingw by configure tests cannot be executed.
[PR9505] For compiling, I saw a warning, in llvm-bcanalyzer.cpp.
(fixed in r127858)

* RC1 3-stage build

Please note configure and cmake will set optimizer option to -O2 by
default even if clang++ were used.
I overwrote for clang --with-optimize-option=-O3.

Generated clang would be stable. But stage2-bin and stage3-bin will
not match. Investigating.
[PR6270] Without r127723, generated clang would be unavailable for
parallel build.
[PR9505] With -Asserts, I saw more two warnings,
lib/Analysis/LazyValueInfo.cpp and

* RC1 with patches.

I have committed many patches for MSYS and mingw. With them, clang and
llvm can pass tests without any failures.
(On TOT, we can run mingw tests without failures!)

  - r127239, r127240 Availability of Lit on MSYS configure.
  - r127723 [PR6270] PathV1::makeUnique()
  - r127726 Fix failure in test/Other/close-stderr.ll on Windows 7
  - r127730 [PR9234] Fix test/CodeGen/X86/dyn-stackalloc.ll with MSYS bash
  - r127731, r127732, r127733, r127734, r127775 [PR9234]
test/CodeGen/X86 tweaks.
  - r127858 [PR9505] Warning in llvm-bcanalyzer.cpp
  - r127872 [PR6745] format("%e")

  - r127284 Availability of Lit on MSYS configure.
  - r127729 test/Driver/hello.c: Tweak for cygming.
  - r127860, r127861 tweak 2 tests for MSYS bash.