mpic++, mpiexec, mpirun: add pages; mpicc: move to common/ (#17137)

Co-authored-by: Managor <42655600+Managor@users.noreply.github.com>

pages/common/mpic++.md

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+# mpic++
+
+> Open MPI wrapper compiler for C++.
+> See also: `mpirun`.
+> More information: <https://www.open-mpi.org/doc/v3.0/man1/mpic++.1.php>.
+
+- Compile an Open MPI program:
+
+`mpic++ {{path/to/source_file}}`
+
+- Show all the wrapper-supplied flags:
+
+`mpic++ --showme`

pages/common/mpiexec.md

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+# mpiexec
+
+> This command is an alias of `mpirun`.
+
+- View documentation for the original command:
+
+`tldr mpirun`

pages/common/mpirun.md

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+# mpirun
+
+> Execute serial and parallel jobs in Open MPI.
+> See also: `mpic++`.
+> More information: <https://docs.open-mpi.org/en/main/man-openmpi/man1/mpirun.1.html>.
+
+- Execute an Open MPI program:
+
+`mpirun {{path/to/executable}}`
+
+- Execute an Open MPI program with `n` parallel processes:
+
+`mpirun -n {{n}} {{path/to/executable}}`
+
+- Allow more processes than available physical cores:
+
+`mpirun -oversubscribe {{path/to/executable}}`