fix %zu support under minGW

and relevant test on Appveyor

lib/Makefile

@@ -19,6 +19,9 @@ LIBVER := $(shell echo $(LIBVER_SCRIPT))
 VERSION?= $(LIBVER)
 
 CPPFLAGS+= -I. -I./common -DXXH_NAMESPACE=ZSTD_
+ifeq ($(OS),Windows_NT)   # MinGW assumed
+CPPFLAGS   += -D__USE_MINGW_ANSI_STDIO   # compatibility with %zu formatting
+endif
 CFLAGS  ?= -O3
 DEBUGFLAGS = -Wall -Wextra -Wcast-qual -Wcast-align -Wshadow \
             -Wstrict-aliasing=1 -Wswitch-enum -Wdeclaration-after-statement \
@@ -52,11 +55,11 @@ ifeq ($(ZSTD_LIB_DECOMPRESSION), 0)
 endif
 
 ifneq ($(ZSTD_LIB_COMPRESSION), 0)
-	ZSTD_FILES += $(ZSTDCOMP_FILES) 
+	ZSTD_FILES += $(ZSTDCOMP_FILES)
 endif
 
 ifneq ($(ZSTD_LIB_DECOMPRESSION), 0)
-	ZSTD_FILES += $(ZSTDDECOMP_FILES) 
+	ZSTD_FILES += $(ZSTDDECOMP_FILES)
 endif
 
 ifneq ($(ZSTD_LIB_DEPRECATED), 0)