Fix compilation on Linux.

Makefile

@@ -1,12 +1,20 @@
+# cut is necessary for Cygwin
+PLATFORM_OS := $(shell uname | cut -d_ -f1)
+
 all: bin2png png2bin
 
 clean:
 	@rm -rf *.o bin2png png2bin
 
-CFLAGS = -std=c99 -Wall -Wextra
+CFLAGS = -D_XOPEN_SOURCE=600 -std=c99 -Wall -Wextra
 LDFLAGS = -lpng
 
+ifeq ($(PLATFORM_OS), Linux)
+	LDFLAGS += -lm # required for sqrt()
+endif
+
 common.o: common.h
+	echo $(PLATFORM_OS)
 	clang -o $@ -c common.c $(CFLAGS)
 
 imgify.o: imgify.h
@@ -16,4 +24,4 @@ bin2png: common.o imgify.o
 	clang -o $@ bin2png.c $^ $(CFLAGS) $(LDFLAGS)
 
 png2bin: common.o imgify.o
-	clang -o $@ png2bin.c $^ $(CFLAGS) $(LDFLAGS)
+	clang -o $@ png2bin.c $^ $(CFLAGS) $(LDFLAGS)

common_main.h

@@ -4,6 +4,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <fcntl.h>
+#include <unistd.h>
 #include <sys/mman.h>
 
 int main(int argc, char *argv[]) {

imgify.c

@@ -22,6 +22,7 @@
 #include <assert.h>
 #include <errno.h>
 #include <stdbool.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>