lib, programs: include common_defs.h by relative path

It's better to use a relative path, so that people not using the
Makefile don't have to put -Icommon on their compiler command line.

Makefile

@@ -45,7 +45,7 @@ cc-option = $(shell if $(CC) $(1) -c -x c /dev/null -o /dev/null \
 	      1>&2 2>/dev/null; then echo $(1); fi)
 
 override CFLAGS :=							\
-	-O2 -fomit-frame-pointer $(CFLAGS) -std=c99 -I. -Icommon	\
+	-O2 -fomit-frame-pointer $(CFLAGS) -std=c99 -I.			\
 	-Wall -Wundef							\
 	$(call cc-option,-Wpedantic)					\
 	$(call cc-option,-Wdeclaration-after-statement)			\

Makefile.msc

@@ -10,7 +10,7 @@
 CC = cl
 LD = link
 AR = lib
-CFLAGS = /MD /O2 -I. -Icommon
+CFLAGS = /MD /O2 -I.
 LDFLAGS =
 
 STATIC_LIB = libdeflatestatic.lib

lib/lib_common.h

@@ -12,7 +12,7 @@
 
 #define BUILDING_LIBDEFLATE
 
-#include "common_defs.h"
+#include "../common/common_defs.h"
 
 /*
  * Prefix with "_libdeflate_" all global symbols which are not part of the API

programs/prog_util.h

@@ -39,7 +39,7 @@
 #include <stdlib.h>
 #include <string.h>
 
-#include "common_defs.h"
+#include "../common/common_defs.h"
 
 #ifdef __GNUC__
 # define _printf(str_idx, args_idx)	\