Failed to build Boost using msvc-14.2 (address-model=64) with ICU enabled

I found that `boost` cannot be compiled correctly with ICU supports on Windows with Visual Studio 2019. Actually, I am using Conan to manage the packages, so ICU should be available. Here is the command issued by Conan:

```text
> C:\Users\laitingsheng\.conan\data\b2\4.2.0\_\_\package\456f15897172eef340fcbac8a70811f2beb26a93\bin\b2.exe target-os=windows architecture=x86 address-model=64 binary-format=pe abi=ms --layout=system --user-config=C:\.conan\9d68ed\1\source_subfolder\tools\build\user-config.jam -sNO_ZLIB=0 -sNO_BZIP2=0 -sNO_LZMA=0 -sNO_ZSTD=0 -sICU_PATH=C:\Users\laitingsheng\.conan\data\icu\67.1\_\_\package\3f7cbf23e8a09e5a013f3be0b9f2ec8486fc6a71 boost.locale.iconv=off boost.locale.icu=on define=MINIZIP_DLL runtime-link=shared threading=multi link=shared variant=release --without-python toolset=msvc segmented-stacks=on define=BOOST_USE_SEGMENTED_STACKS=1 define=BOOST_USE_UCONTEXT=1 pch=on install --prefix=C:\.conan\efe744\1 -j36 --abbreviate-paths --debug-configuration --build-dir="C:\.conan\1b56b9\1"
```

And obviously, `-sICU_PATH` was specified correctly. But `b2` gives the following output

```text
...

- has_icu builds : no

...

- icu : no
- icu (lib64) : no

...
```

When I read the `config.log` file under the build directory, I surprisingly found that it only tried to use `ICU_PATH/lib64` and `ICU_PATH/bin64` but never `ICU_PATH/lib` and `ICU_PATH/bin`:

```text
...

compile-c-c++ C:\.conan\1b56b9\1\boost\bin.v2\libs\locale\build\msvc-14.2\dbg\adrs-mdl-64\thrd-mlt\has_icu_obj.obj
has_icu_test.cpp
msvc.link C:\.conan\1b56b9\1\boost\bin.v2\libs\locale\build\msvc-14.2\dbg\adrs-mdl-64\thrd-mlt\has_icu.exe
LINK : fatal error LNK1181: cannot open input file 'icudt.lib'

call "C:\.conan\1b56b9\1\boost\bin.v2\standalone\msvc\msvc-14.2\adrs-mdl-64\archt-x86\msvc-setup.bat" >nul
link /NOLOGO /INCREMENTAL:NO /DEBUG /MACHINE:X64 /MANIFEST /subsystem:console /out:"C:\.conan\1b56b9\1\boost\bin.v2\libs\locale\build\msvc-14.2\dbg\adrs-mdl-64\thrd-mlt\has_icu.exe" /LIBPATH:"C:\Users\laitingsheng\.conan\data\icu\67.1\_\_\package\3f7cbf23e8a09e5a013f3be0b9f2ec8486fc6a71\bin64" /LIBPATH:"C:\Users\laitingsheng\.conan\data\icu\67.1\_\_\package\3f7cbf23e8a09e5a013f3be0b9f2ec8486fc6a71\lib64" @"C:\.conan\1b56b9\1\boost\bin.v2\libs\locale\build\msvc-14.2\dbg\adrs-mdl-64\thrd-mlt\has_icu.exe.rsp"
if %ERRORLEVEL% NEQ 0 EXIT %ERRORLEVEL%

...failed msvc.link C:\.conan\1b56b9\1\boost\bin.v2\libs\locale\build\msvc-14.2\dbg\adrs-mdl-64\thrd-mlt\has_icu.exe C:\.conan\1b56b9\1\boost\bin.v2\libs\locale\build\msvc-14.2\dbg\adrs-mdl-64\thrd-mlt\has_icu.pdb...
...failed updating 2 targets...

...
```

But in my understanding, `has_icu` should also query `ICU_PATH/lib` and `ICU_PATH/bin` to determine if `icu` exists. `ICU_PATH/lib64` and `ICU_PATH/bin64` is only for `icu (lib64)`.

I think issue #620 is somewhat similar to this problem, and it has been posted for nearly 1 year without a reply.

conan-io/conan-center-index#1704 proposed a fix to patch the `libs/locale/build/Jamfile.v2` file, but it appears to be an aggressive approach to resolve this issue.

Start with libs/locale/build/Jamfile.v2 and the has_icu probe described in the issue, then reproduce the supplied b2 command and inspect config.log. Done means ICU detection succeeds with the reported Conan directory layout, including the appropriate lib/bin paths, instead of reporting has_icu and icu as unavailable.

Written by the indexing model from the issue text.