use distinct var for top_level

<PROJECT_NAME>_IS_TOP_LEVEL is not externally overridable,
even with CMAKE_CACHE_ARGS

cmake/lapack.cmake

@@ -1,7 +1,7 @@
 include(GNUInstallDirs)
 include(ExternalProject)
 
-if(NOT PROJECT_IS_TOP_LEVEL)
+if(NOT SCALAPACK_IS_TOP_LEVEL)
   message(STATUS "${PROJECT_NAME} ${PROJECT_VERSION} deferring to ${CMAKE_PROJECT_NAME} for LAPACK")
   return()
 endif()

options.cmake

@@ -1,3 +1,7 @@
+if(DEFINED SCALAPACK_IS_TOP)
+  set(SCALAPACK_IS_TOP_LEVEL ${SCALAPACK_IS_TOP})
+endif()
+
 if(local)
   get_filename_component(local ${local} ABSOLUTE)
 
@@ -33,6 +37,6 @@ list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_LIST_DIR}/cmake)
 # Necessary for shared library with Visual Studio / Windows oneAPI
 set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS true)
 
-if(CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT AND PROJECT_IS_TOP_LEVEL)
+if(CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT AND SCALAPACK_IS_TOP_LEVEL)
   set(CMAKE_INSTALL_PREFIX ${PROJECT_BINARY_DIR}/local CACHE PATH "Install path" FORCE)
 endif()