CMake: enable setting default dir creation permissions

Introduces CMAKE_DEFAULT_DIRECTORY_INSTALL_PERMISSIONS
variable which enables the user to specify the default
permissions for directory creation. This setting is then
used to auto set the permissions on directories which
are implicitly created by install() and file(INSTALL)
commands such as CMAKE_INSTALL_PREFIX directories.

Source/cmLocalGenerator.cxx

@@ -487,6 +487,20 @@ void cmLocalGenerator::GenerateInstallRules()
     /* clang-format on */
   }
 
+  // Write default directory permissions.
+  if (const char* defaultDirPermissions = this->Makefile->GetDefinition(
+        "CMAKE_INSTALL_DEFAULT_DIRECTORY_PERMISSIONS")) {
+    /* clang-format off */
+    fout <<
+      "# Set default install directory permissions.\n"
+      "if(NOT DEFINED CMAKE_INSTALL_DEFAULT_DIRECTORY_PERMISSIONS)\n"
+      "  set(CMAKE_INSTALL_DEFAULT_DIRECTORY_PERMISSIONS \""
+         << defaultDirPermissions << "\")\n"
+      "endif()\n"
+      "\n";
+    /* clang-format on */
+  }
+
   // Ask each install generator to write its code.
   std::vector<cmInstallGenerator*> const& installers =
     this->Makefile->GetInstallGenerators();