move flag definition to dynamic_loader.cc

Author: mikethegoblin

paddle/phi/backends/dynload/dynamic_loader.cc

@@ -72,6 +72,13 @@ PHI_DEFINE_string(rccl_dir,
 COMMON_DECLARE_string(flagcx_dir);
 #endif
 
+PHI_DEFINE_EXPORTED_string(
+  flagcx_dir,  // NOLINT
+  "",
+  "Specify path for loading libflagcx.so. For instance, "
+  "For instance, /usr/local/flagcx/lib. If default, "
+  "dlopen will search flagcx from LD_LIBRARY_PATH");
+
 #ifdef PADDLE_WITH_XPU
 PD_DEFINE_string(xpti_dir, "", "Specify path for loading libxpti.so.");
 #endif