CMake: avoid use of 'GETOPT_INCLUDE_DIRS' when getopt has not been looked for

When running CMake with `--warn-uninitialized -Werror=dev`, this prevents the
following:

  CMake Error (dev) at cmd/mingle/CMakeLists.txt:15 (target_include_directories):
    uninitialized variable 'GETOPT_INCLUDE_DIRS'

Gitlab: #2291

diff --git a/cmd/mingle/CMakeLists.txt b/cmd/mingle/CMakeLists.txt
index 3a88113491bb42678f7d1ef5687647685b2858b0..077c63a6dfc1cae7078fcdbb90ffa4281f3c3056 100644 (file)
--- a/cmd/mingle/CMakeLists.txt
+++ b/cmd/mingle/CMakeLists.txt
@@ -12,10 +12,12 @@ if(with_sfdp AND ANN_FOUND)
       ../../lib/common
   )
 
-  target_include_directories(mingle
-    SYSTEM PRIVATE
-      ${GETOPT_INCLUDE_DIRS}
-  )
+  if(GETOPT_FOUND)
+    target_include_directories(mingle
+      SYSTEM PRIVATE
+        ${GETOPT_INCLUDE_DIRS}
+    )
+  endif()
 
   target_link_libraries(mingle
     cdt