The previous quoting caused "make -C src/bin check" to ignore, rather
than add to, any LD_LIBRARY_PATH content from the environment.
Back-patch to 9.4, where the macro was introduced.
# prepend to path if already set, else just set it
define add_to_path
-$(1)='$(if $($(1)),$(2):$$$(1),$(2))'
+$(1)="$(if $($(1)),$(2):$$$(1),$(2))"
endef
# platform-specific environment variable to set shared library path