build: add support for fixing up library soname

This makes it possible to declare a package ABI_VERSION independent from the
upstream soname by setting PKG_ABI_VERSION in the package makefile.
The library filename is fixed up for files installed to packages and to the
staging dir. References to the original from executables within the same
package are also fixed up

Signed-off-by: Felix Fietkau <nbd@nbd.name>

rules.mk

@@ -339,6 +339,10 @@ else
     $(SCRIPT_DIR)/rstrip.sh
 endif
 
+SET_ABI_VERSION= \
+    PATCHELF="$(STAGING_DIR_HOST)/bin/patchelf" \
+	$(SCRIPT_DIR)/set-abi-version.sh
+
 ifeq ($(CONFIG_IPV6),y)
   DISABLE_IPV6:=
 else
@@ -428,6 +432,8 @@ $(shell \
 )
 endef
 
+abi_version_str = $(subst -,,$(subst _,,$(subst .,,$(1))))
+
 COMMITCOUNT = $(if $(DUMP),0,$(call commitcount))
 AUTORELEASE = $(if $(DUMP),0,$(call commitcount,1))