Update CMakeLists.txt

Co-authored-by: Cristian Le <github@lecris.me>

Author: flagarde

CMakeLists.txt

@@ -46,7 +46,7 @@ if(NOT ${CMAKE_PROJECT_NAME} STREQUAL ${PROJECT_NAME})
   find_package(CPM CONFIG REQUIRED NO_POLICY_SCOPE)
 endif()
 
-if(CPM_INSTALL)
+if (NOT CMAKE_PROJECT_NAME STREQUAL PROJECT_NAME)
   # Without it : Unable to determine default CMAKE_INSTALL_LIBDIR directory because no target
   # architecture is known.  Please enable at least one language before including GNUInstallDirs.
   enable_language(C)