cmake: set os2 dll name to 'physfs'

not libphysfs, because of os2 limitation.

CMakeLists.txt

@@ -179,6 +179,9 @@ if(PHYSFS_BUILD_SHARED)
     if(WINRT)
 		set_target_properties(physfs PROPERTIES VS_WINRT_COMPONENT True)
     endif()
+    if(OS2) # OS/2 does not support a DLL name longer than 8 characters.
+        set_target_properties(physfs PROPERTIES OUTPUT_NAME "physfs")
+    endif()
     target_link_libraries(physfs ${OPTIONAL_LIBRARY_LIBS} ${OTHER_LDFLAGS})
     set(PHYSFS_LIB_TARGET physfs)
     set(PHYSFS_INSTALL_TARGETS ${PHYSFS_INSTALL_TARGETS} ";physfs")