gbuild: fix gb_Library_set_soversion_script

so it does nothing on platforms where soversions are not used

solenv/gbuild/Library.mk

@@ -77,9 +77,7 @@ $(call gb_Deliver_add_deliverable,$(call gb_Library_get_target,$(1)),$(call gb_L
 
 endef
 
-define gb_Library_set_soversion_script
-$(if $(2),,$(call gb_Output_error,gb_Library_set_soversion_script: no version))
-$(if $(3),,$(call gb_Output_error,gb_Library_set_soversion_script: no script))
+define gb_Library__set_soversion_script
 $(call gb_LinkTarget_get_target,$(call gb_Library_get_linktargetname,$(1))) : \
 	$(3)
 $(call gb_Library_get_target,$(1)) : SOVERSION := $(2)
@@ -91,6 +89,14 @@ $(call gb_LinkTarget_set_auxtargets,$(call gb_Library_get_linktargetname,$(1)),\
 	$(call gb_LinkTarget_get_target,$(call gb_Library_get_linktargetname,$(1))).$(2))
 endef
 
+# for libraries that maintain stable ABI: set SOVERSION and version script
+# $(call gb_Library_set_soversion_script,soversion,versionscript)
+define gb_Library_set_soversion_script
+$(if $(2),,$(call gb_Output_error,gb_Library_set_soversion_script: no version))
+$(if $(3),,$(call gb_Output_error,gb_Library_set_soversion_script: no script))
+$(call gb_Library__set_soversion_script_platform,$(1),$(2),$(3))
+endef
+
 define gb_Library_set_componentfile
 $(call gb_ComponentTarget_ComponentTarget,$(2),$(call gb_Library__get_componentprefix,$(1)),\
 	$(call gb_Library_get_runtime_filename,$(if $(MERGELIBS),$(if $(filter $(gb_MERGED_LIBS),$(1)),merged,$(1)),$(1))))

solenv/gbuild/platform/macosx.mk

@@ -299,6 +299,8 @@ $(call gb_LinkTarget_get_target,$(2)) : LAYER := $(call gb_Library_get_layer,$(1
 
 endef
 
+gb_Library__set_soversion_script_platform = $(gb_Library__set_soversion_script)
+
 
 # StaticLibrary class
 

solenv/gbuild/platform/unxgcc.mk

@@ -313,6 +313,8 @@ $(call gb_LinkTarget_get_target,$(2)) : RPATH := $(call gb_Library_get_rpath,$(1
 
 endef
 
+gb_Library__set_soversion_script_platform = $(gb_Library__set_soversion_script)
+
 
 # StaticLibrary class