Add SOVERSION to libobs-opengl

Because libobs-opengl is a public library, it's customary to have SONAME
embedded in the library file.  Also remove the prefix override and
remove the prefixing "lib" from the output name.  This also requires us
to pass the library file name to dlopen invocations.

cmake/Modules/ObsHelpers.cmake

@@ -516,3 +516,20 @@ function(install_obs_plugin_with_data target datadir)
 	install_obs_plugin(${target})
 	install_obs_data(${target} "${datadir}" "obs-plugins/${target}")
 endfunction()
+
+function(define_graphic_modules target)
+	foreach(dl_lib opengl d3d9 d3d11)
+		string(TOUPPER ${dl_lib} dl_lib_upper)
+		if(TARGET libobs-${dl_lib})
+			target_compile_definitions(${target}
+				PRIVATE
+				DL_${dl_lib_upper}="$<TARGET_FILE_NAME:libobs-${dl_lib}>"
+				)
+		else()
+			target_compile_definitions(${target}
+				PRIVATE
+				DL_${dl_lib_upper}=""
+				)
+		endif()
+	endforeach()
+endfunction()