sci-physics/SU2: restrict with MPI 3.1 impl. Add custom-mpi option

Meson.build script isn't properly detect mpich as MPI impl.,
therefore meson option 'custom-mpi' is used now with export
of CC=mpicc and CXX=mpicxx as compilers.

Mpi implementations is restricted with MPI 3.1 within ebuild.

FEATURES="-network-sandbox" could be required to run tests
for some mpi implementations/versions.

Closes: https://bugs.gentoo.org/819060

Signed-off-by: Sergey Torokhov <torokhov-s-a@yandex.ru>

sci-physics/SU2/SU2-7.2.0.ebuild

@@ -35,7 +35,7 @@ REQUIRED_USE="
 
 RDEPEND="
 	${PYTHON_DEPS}
-	mpi? ( virtual/mpi[cxx] )
+	mpi? ( || ( >=sys-cluster/openmpi-1.10.7[cxx] >=sys-cluster/mpich-3.3[cxx] ) )
 	mkl? ( sci-libs/mkl )
 	openblas? ( sci-libs/openblas )
 "
@@ -87,6 +87,11 @@ src_prepare(){
 }
 
 src_configure() {
+	if use mpi ; then
+		export CC=mpicc
+		export CXX=mpicxx
+	fi
+
 	local emesonargs=(
 		-Denable-autodiff=false
 		-Denable-directdiff=false
@@ -94,6 +99,7 @@ src_configure() {
 		-Denable-pywrapper=false
 		-Dwith-omp=false
 		$(meson_feature mpi with-mpi)
+		$(meson_use mpi custom-mpi)
 		$(meson_use cgns enable-cgns)
 		$(meson_use mkl enable-mkl)
 		$(meson_use mpp enable-mpp)