One test fails after runtest graph_parallel submodule on x86 paltform.

[JunchenMeteor]

Environment:
VS 2019 + Windows Server 2016

Issue description:
One test fails after runtest graph_parallel submodule on x86 paltform. Could you please take a look?

Reproduce steps:
git clone ​https://github.com/boostorg/boost.git F:\gitP\boostorg\boost
git -C "F:\gitP\boostorg\boost" submodule update --init --recursive
.\b2 headers variant=release --build-dir=..\out\x86rel address-model=32
.\b2 -j16 variant=release --build-dir=..\out\x86rel libs\graph_parallel\test
test_38.log

ErrorMessage:
compile-c-c++ ..\out\x86rel\boost\bin.v2\libs\graph_parallel\example\msvc-14.2\release\threading-multi\breadth_first_search.obj
breadth_first_search.cpp
.\boost/mpi/config.hpp(22): fatal error C1083: Cannot open include file: 'mpi.h': No such file or directory (d:\a01_work\4\s\src\vctools\Compiler\CxxFE\sl\p1\c\p0prepro.c:1964)

...failed compile-c-c++ ..\out\x86rel\boost\bin.v2\libs\graph_parallel\example\msvc-14.2\release\threading-multi\breadth_first_search.obj...

compile-c-c++ ..\out\x86rel\boost\bin.v2\libs\graph_parallel\example\msvc-14.2\release\threading-multi\dijkstra_shortest_paths.obj
dijkstra_shortest_paths.cpp
.\boost/mpi/config.hpp(22): fatal error C1083: Cannot open include file: 'mpi.h': No such file or directory (d:\a01_work\4\s\src\vctools\Compiler\CxxFE\sl\p1\c\p0prepro.c:1964)

...failed compile-c-c++ ..\out\x86rel\boost\bin.v2\libs\graph_parallel\example\msvc-14.2\release\threading-multi\dijkstra_shortest_paths.obj...

[jeking3]

It looks like you did not provide the proper location to the mpi header.

Take a look at https://github.com/boostorg/build/blob/dca10cf20759b0d194f8305356bf155cc5632c0e/src/tools/mpi.jam and see if that helps you get to a resolution.

[jeremy-murphy]

@qd1332543 , if you still use this library, it is in desperate need of help to fix existing infrastructure problems, so I am calling on all users to please help if they can.