Move C/C++ sources to src subdirectory

src/fio_headers.h

@@ -0,0 +1,16 @@
+extern "C" {
+// Kill atomics in fio headers
+#define _STDATOMIC_H
+#include "fio/arch/arch.h"
+
+#undef atomic_load_acquire
+#undef atomic_store_release
+#define atomic_load_acquire(p) *(p)
+#define atomic_store_release(p, v) (*(p)) = (v)
+
+#define CONFIG_HAVE_GETTID
+#define CONFIG_SYNC_FILE_RANGE
+#define CONFIG_PWRITEV2
+#include "fio/fio.h"
+#include "fio/optgroup.h"
+}