oss-fuzz: Add fuzzing headers

These includes header files were taken from:

    https://github.com/guidovranken/fuzzing-headers.git

with some minor changes required to make them compile cleanly
with the extra compiler warning flags used by the FLAC build
system.

oss-fuzz/fuzzing/memory.hpp

@@ -0,0 +1,73 @@
+#pragma once
+
+#include <stdio.h>
+#include <optional>
+
+#ifndef ASAN
+#define ASAN 0
+#endif
+
+#ifndef MSAN
+#define MSAN 0
+#endif
+
+namespace fuzzing {
+namespace memory {
+
+#ifndef FUZZING_HEADERS_NO_IMPL
+#if ASAN == 1
+extern "C" void *__asan_region_is_poisoned(const void *beg, size_t size);
+#endif
+
+#if MSAN == 1
+extern "C" void __msan_check_mem_is_initialized(const volatile void *x, size_t size);
+#endif
+
+void memory_test_asan(const void* data, const size_t size)
+{
+    (void)data;
+    (void)size;
+
+#if ASAN == 1
+    if ( __asan_region_is_poisoned(data, size) != NULL ) {
+        abort();
+    }
+#endif
+}
+
+void memory_test_msan(const void* data, const size_t size)
+{
+    (void)data;
+    (void)size;
+
+#if MSAN == 1
+    __msan_check_mem_is_initialized(data, size);
+#endif
+}
+
+void memory_test(const void* data, const size_t size)
+{
+    memory_test_asan(data, size);
+    memory_test_msan(data, size);
+}
+
+template <class T>
+void memory_test(const T& t)
+{
+    (void)t;
+}
+
+template <>
+void memory_test(const std::string& s)
+{
+    (void)s;
+
+#if MSAN == 1
+    memory_test(s.data(), s.size());
+#endif
+}
+
+#endif
+
+} /* namespace memory */
+} /* namespace fuzzing */