librdmacm/preload.c: fix duplicate LFS symbols definitions

85f9747 introduces the preload of fcntl64 and it fails to build on armhf:

Assembler messages:
 Error: symbol `__fcntl_time64' is already defined
 Error: symbol `sendfile64' is already defined

On armhf (and potentially other 32 bits systems), glibc directs fcntl64
and fcntl to the same symbol name. preload.c defines both fcntl and fcntl64
and these 2 implementations are in fact tight to the same symbol, that causes
the double symbol error.

So only provide the definition of both fcntl and fcntl64 if they are 2
separate symbols.

This fixes the issue both for sendfile64 and fcntl64.

Fixes: 85f9747 ("librdmacm: Add support for fcntl64")
Signed-off-by: Hector Cao <hector.cao@canonical.com>

Author: hector-cao

CMakeLists.txt

@@ -467,9 +467,17 @@ int main(void) {
   return 0;
 }
 " RDMA_PRELOAD_LIBC_HAS_FCNTL64_SENDFILE64)
+CHECK_C_SOURCE_COMPILES("
+#include <fcntl.h>
+int fcntl(int, int, ...) { return 0; }
+int fcntl64(int, int, ...) { return 0; }
+int main(void) {
+  return 0;
+}
+" RDMA_PRELOAD_LIBC_SYMS_LFS_NOT_ALIAS)
 set(CMAKE_REQUIRED_DEFINITIONS "${SAFE_CMAKE_REQUIRED_DEFINITIONS}")
 set(CMAKE_REQUIRED_QUIET 0)
-if(RDMA_PRELOAD_LIBC_HAS_FCNTL64_SENDFILE64)
+if(RDMA_PRELOAD_LIBC_HAS_FCNTL64_SENDFILE64 AND RDMA_PRELOAD_LIBC_SYMS_LFS_NOT_ALIAS)
   set(RDMA_PRELOAD_HAVE_LFS_WRAPPER_SYMS 1)
 else()
   set(RDMA_PRELOAD_HAVE_LFS_WRAPPER_SYMS 0)