Extend the configure test for C++17 filesystem

If recent versions of libc++ are built with filesystem support disabled,
the filesystem header still is installed., The std::filesystem::path()
constructor is completely defined inline in that header, making the test
pass on such configurations, despite C++17 filesystem not being
implemented.

Test a call to std::filesystem::copy instead, which requires the actual
library implementation to be available as well (on recent libc++).

Change-Id: Id997ab75f3299d8431b13cad871f2901f4d9f6ed
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/corelib/configure.cmake

@@ -165,7 +165,9 @@ int main(int argc, char **argv)
 {
     (void)argc; (void)argv;
     /* BEGIN TEST: */
-std::filesystem::path p(\"./file\");
+std::filesystem::copy(
+    std::filesystem::path("./file"),
+    std::filesystem::path("./other"));
     /* END TEST: */
     return 0;
 }

src/corelib/configure.json

@@ -371,7 +371,11 @@
             "type": "compile",
             "test": {
                 "include": "filesystem",
-                "main": "std::filesystem::path p(\"./file\");",
+                "main": [
+                    "std::filesystem::copy(",
+                    "    std::filesystem::path(\"./file\"),",
+                    "    std::filesystem::path(\"./other\"));"
+                ],
                 "qmake": "CONFIG += c++17"
             }
         },