default rule is `lib-release`
`lib-release` wasn't working : it was just skipped.
Removing `lib-release` from the list of .PHONY targets fixes it.
Same for `lib-mt`.
.PHONY: lib
lib : libzstd.a libzstd
-.PHONY: lib-mt
+# note : do not define lib-mt or lib-release as .PHONY
+# make does not consider implicit pattern rule for .PHONY target
+
%-mt : CPPFLAGS += -DZSTD_MULTITHREAD
%-mt : LDFLAGS += -pthread
%-mt : %
@echo multi-threading build completed
-.PHONY: lib-release
%-release : DEBUGFLAGS :=
%-release : %
@echo release build completed