build: fix Windows small-icu build with ClangCL - #64263

Both routes advanced and each hit one thing.

conda-clang-cl (ninja) compiled 500 edges with clang-cl 21.1.8 -- ICU,
the host tools, the builtins library found and on the link line -- and
stopped in v8_libbase at v8config.h: "C++20 or later required." Two
causes, both needed fixing:

- gyp's ninja generator appends CFLAGS, CXXFLAGS and LDFLAGS from the
  environment after its own flags, and conda's clang-cl activation
  exports /std:c++17 in CXXFLAGS, which then outranked whatever V8 said.
  bld.bat now strips /std:, -std and -fuse-ld= from those, and clears
  LDFLAGS: the `-Xlinker /DEFAULTLIB:...` there is clang-driver syntax
  that link.exe answered with LNK4044, and patch 0104 already links the
  builtins library in a form it understands. build.sh strips -std= for
  the same reason.
- Even with a clean environment there was no /std: at all: with clang,
  common.gypi expresses the standard as the MSBuild-only property
  LanguageStandard (stdcpp20), and gyp's ninja emulation has no case for
  it. Patch 0106 adds one, per language -- C files get /std:c11, not
  c++20, which clang-cl would refuse where cl.exe ignores it. Verified
  on Windows ninja files generated here (gyp's ninja-win flavour, with
  its registry probes stubbed): cflags_cc = /TP /std:c++20, cflags_c =
  /std:c11, and the MSVC branch's -std:c++20 gone.

vs-clang-cl (MSBuild) built ICU's tools with Visual Studio's clang-cl
22.1.3 and stopped writing the ICU data object:

  genccode: CPU architecture must be set for Clang-CL

A genccode compiled by clang will not infer the machine type from its
own macros, and node's small-icu action for Windows never passed -c.
Node's Windows builds are full-icu, so nobody hit it until now; the fix
is nodejs/node#64263, after 26.6.0, and patch 0107 is that one line. The
ninja route runs the same action and would have reached it too.

Also caught before it could fail: v8config.h guards on __cplusplus, which
cl.exe reports as 199711L unless given /Zc:__cplusplus. The consumer test
compiles with cl.exe on Windows, so it gets the flag.

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01KzqRnuUy9dpMik6sxVaKXd