Update lib Makefile to have new targets

lib/Makefile

@@ -8,6 +8,9 @@
 # You may select, at your option, one of the above-listed licenses.
 # ################################################################
 
+# Note: by default, the dynamic library is built single-threaded and static library is built
+# multi-threaded. It is possible to force multi or single threaded builds by appending
+# -mt or -nomt to the build target (like lib-mt for multi-threaded, lib-nomt for single-threaded).
 .PHONY: default
 default: lib-release
 
@@ -166,6 +169,14 @@ endif
 endif
 CPPFLAGS  += -DZSTD_LEGACY_SUPPORT=$(ZSTD_LEGACY_SUPPORT)
 
+CPPFLAGS_MT     := $(CPPFLAGS) -DZSTD_MULTITHREAD
+CPPFLAGS_NOMT   := $(CPPFLAGS)
+CPPFLAGS_DYNLIB := $(CPPFLAGS_MT) # dynamic library build defaults to multithreading
+
+LDFLAGS_MT     := $(LDFLAGS) -pthread
+LDFLAGS_NOMT   := $(LDFLAGS)
+LDFLAGS_DYNLIB := $(LDFLAGS_MT)
+
 ZSTD_LOCAL_SRC := $(notdir $(ZSTD_FILES))
 ZSTD_LOCAL_OBJ := $(ZSTD_LOCAL_SRC:.c=.o)
 
@@ -238,7 +249,11 @@ ZSTD_STATLIB_OBJ := $(addprefix $(ZSTD_STATLIB_DIR)/,$(ZSTD_LOCAL_OBJ))
 $(ZSTD_STATLIB): ARFLAGS = rcs
 $(ZSTD_STATLIB): | $(ZSTD_STATLIB_DIR)
 $(ZSTD_STATLIB): $(ZSTD_STATLIB_OBJ)
-	@echo compiling static library
+ifneq (,$(findstring -DZSTD_MULTITHREAD,$(CPPFLAGS)))
+	@echo compiling multi-threaded static library $(LIBVER)
+else
+	@echo compiling single-threaded static library $(LIBVER)
+endif
 	$(AR) $(ARFLAGS) $@ $^
 
 libzstd.a: $(ZSTD_STATLIB)
@@ -257,7 +272,9 @@ else  # not Windows
 
 LIBZSTD = libzstd.$(SHARED_EXT_VER)
 .PHONY: $(LIBZSTD)  # must be run every time
-$(LIBZSTD): CFLAGS += -fPIC -fvisibility=hidden
+$(LIBZSTD): CPPFLAGS = $(CPPFLAGS_DYNLIB)
+$(LIBZSTD): LDFLAGS  = $(LDFLAGS_DYNLIB)
+$(LIBZSTD): CFLAGS  += -fPIC -fvisibility=hidden
 $(LIBZSTD): LDFLAGS += -shared
 
 ifndef BUILD_DIR
@@ -275,7 +292,11 @@ ZSTD_DYNLIB_OBJ := $(addprefix $(ZSTD_DYNLIB_DIR)/,$(ZSTD_LOCAL_OBJ))
 
 $(ZSTD_DYNLIB): | $(ZSTD_DYNLIB_DIR)
 $(ZSTD_DYNLIB): $(ZSTD_DYNLIB_OBJ)
-	@echo compiling dynamic library $(LIBVER)
+ifneq (,$(findstring -DZSTD_MULTITHREAD,$(CPPFLAGS)))
+	@echo compiling multi-threaded dynamic library $(LIBVER)
+else
+	@echo compiling single-threaded dynamic library $(LIBVER)
+endif
 	$(CC) $(FLAGS) $^ $(LDFLAGS) $(SONAME_FLAGS) -o $@
 	@echo creating versioned links
 	ln -sf $@ libzstd.$(SHARED_EXT_MAJOR)
@@ -300,7 +321,12 @@ lib : libzstd.a libzstd
 %-mt : CPPFLAGS += -DZSTD_MULTITHREAD
 %-mt : LDFLAGS  += -pthread
 %-mt : %
-	@echo multi-threading build completed
+	@echo multi-threaded build completed
+
+%-nomt : CPPFLAGS_DYNLIB := $(CPPFLAGS_NOMT)
+%-nomt : LDFLAGS_DYNLIB  := $(LDFLAGS_NOMT)
+%-nomt : %
+	@echo single-threaded build completed
 
 %-release : DEBUGFLAGS :=
 %-release : %