fuzz: Simplify definition of fuzzing targets and build them also with gcc

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

tests/fuzz/fuzzer.c

@@ -0,0 +1,39 @@
+/* Simpler gnu89 version of StandaloneFuzzTargetMain.c from LLVM */
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+int LLVMFuzzerTestOneInput (const unsigned char *data, size_t size);
+__attribute__((weak)) int LLVMFuzzerInitialize(int *argc, char ***argv);
+
+int
+main (int argc, char **argv)
+{
+    FILE *f = NULL;
+    size_t n_read, len;
+    unsigned char *buf = NULL;
+
+    if (argc < 2) {
+        return 1;
+    }
+
+    if (LLVMFuzzerInitialize) {
+        LLVMFuzzerInitialize(&argc, &argv);
+    }
+
+    f = fopen (argv[1], "r");
+    assert (f);
+    fseek (f, 0, SEEK_END);
+    len = ftell (f);
+    fseek (f, 0, SEEK_SET);
+    buf = (unsigned char*) malloc (len);
+    n_read = fread (buf, 1, len, f);
+    fclose (f);
+    assert (n_read == len);
+    LLVMFuzzerTestOneInput (buf, len);
+
+    free (buf);
+    printf ("Done!\n");
+    return 0;
+}