AIX: Install ExportImportList script with execute permission

This script was added by commit 0f150b69d3 (AIX: Explicitly compute
shared object exports for both XL and GNU, 2019-07-11,
v3.16.0-rc1~418^2~2) but does not have a `.sh` extension so our existing
install rules neglect to give it execute permission.  Our test suite
works on AIX in the build tree but the script is broken without execute
permission on installation.

Fixes: #20520

CMakeLists.txt

@@ -841,6 +841,10 @@ if(NOT CMake_TEST_EXTERNAL_CMAKE)
     PATTERN "*.sh*" PERMISSIONS OWNER_READ OWNER_EXECUTE OWNER_WRITE
                                 GROUP_READ GROUP_EXECUTE
                                 WORLD_READ WORLD_EXECUTE
+    PATTERN "ExportImportList"
+      PERMISSIONS OWNER_READ OWNER_EXECUTE OWNER_WRITE
+                  GROUP_READ GROUP_EXECUTE
+                  WORLD_READ WORLD_EXECUTE
     REGEX "Help/(dev|guide)($|/)" EXCLUDE
     )