rename fuzz target, add entry point

tests/fuzz_main.c

@@ -0,0 +1,54 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+/* fuzz target entry point, works without libFuzzer */
+
+int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size);
+
+int main(int argc, char **argv)
+{
+    FILE *f;
+    char *buf = NULL;
+    long siz_buf;
+
+    if(argc < 2)
+    {
+        fprintf(stderr, "no input file\n");
+        goto err;
+    }
+
+    f = fopen(argv[1], "rb");
+    if(f == NULL)
+    {
+        fprintf(stderr, "error opening input file %s\n", argv[1]);
+        goto err;
+    }
+
+    fseek(f, 0, SEEK_END);
+
+    siz_buf = ftell(f);
+    rewind(f);
+
+    if(siz_buf < 1) goto err;
+
+    buf = (char*)malloc((size_t)siz_buf);
+    if(buf == NULL)
+    {
+        fprintf(stderr, "malloc() failed\n");
+        goto err;
+    }
+
+    if(fread(buf, (size_t)siz_buf, 1, f) != 1)
+    {
+        fprintf(stderr, "fread() failed\n");
+        goto err;
+    }
+
+    (void)LLVMFuzzerTestOneInput((uint8_t*)buf, (size_t)siz_buf);
+
+err:
+    free(buf);
+
+    return 0;
+}

tests/stb_png_read_fuzzer.c

@@ -2,7 +2,7 @@
 #define STBI_ONLY_PNG
 #include "../stb_image.h"
 
-extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
+int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
 {
     int x, y, channels;