Fix CMake Python IPO Control

`pybind11::lto` is only defined if `CMAKE_INTERPROCEDURAL_OPTIMIZATION`
is not set in `pybind11Common.cmake`. Package managers like Spack
use the latter.

CMakeLists.txt

@@ -455,7 +455,7 @@ endif()
 
 # Interprocedural optimization (IPO) / Link-Time Optimization (LTO)
 if(WarpX_IPO)
-    enable_IPO("${_ALL_TARGETS}")
+    warpx_enable_IPO("${_ALL_TARGETS}")
 endif()
 
 # link dependencies
@@ -488,7 +488,13 @@ foreach(D IN LISTS WarpX_DIMS)
     if(WarpX_PYTHON)
         target_link_libraries(pyWarpX_${SD} PRIVATE pybind11::module pybind11::windows_extras)
         if(WarpX_PYTHON_IPO)
-            target_link_libraries(pyWarpX_${SD} PRIVATE pybind11::lto)
+            if(NOT DEFINED CMAKE_INTERPROCEDURAL_OPTIMIZATION)
+                # conditionally defined target in pybind11
+                # https://github.com/pybind/pybind11/blob/v2.12.0/tools/pybind11Common.cmake#L397-L403
+                target_link_libraries(pyWarpX_${SD} PRIVATE pybind11::lto)
+            else()
+                warpx_enable_IPO(pyWarpX_${SD})
+            endif()
         endif()
     endif()
 

cmake/WarpXFunctions.cmake

@@ -209,7 +209,7 @@ endmacro()
 
 # Enables interprocedural optimization for a list of targets
 #
-function(enable_IPO all_targets_list)
+function(warpx_enable_IPO all_targets_list)
     include(CheckIPOSupported)
     check_ipo_supported(RESULT is_IPO_available)
     if(is_IPO_available)