add library API to print OS/Compiler info (for use with LAMMPS shell)

doc/src/Library_properties.rst

@@ -4,6 +4,7 @@ Retrieving or setting LAMMPS system properties
 This section documents the following functions:
 
 - :cpp:func:`lammps_version`
+- :cpp:func:`lammps_get_os_info`
 - :cpp:func:`lammps_memory_usage`
 - :cpp:func:`lammps_get_mpi_comm`
 - :cpp:func:`lammps_get_natoms`
@@ -80,6 +81,11 @@ sub-domains and processors.
 
 -----------------------
 
+.. doxygenfunction:: lammps_get_os_info
+   :project: progguide
+
+-----------------------
+
 .. doxygenfunction:: lammps_memory_usage
    :project: progguide