libvdwxc: Fix configure with gcc-14 (#45093)

var/spack/repos/builtin/packages/libvdwxc/fftw-detection.patch

@@ -0,0 +1,13 @@
+diff --git a/configure b/configure
+index 494ea9f..1ca6516 100755
+--- a/configure
++++ b/configure
+@@ -17006,7 +17006,7 @@ int
+ main ()
+ {
+ 
+-        fftw_plan *plan;
++        fftw_plan plan;
+         fftw_complex *a1, *a2;
+         fftw_execute_dft(plan, a1, a2);
+ 

var/spack/repos/builtin/packages/libvdwxc/package.py

@@ -54,3 +54,12 @@ def configure_args(self):
             args += ["--without-mpi"]
 
         return args
+
+    # misuse of fftw_plan in m4 for fftw detection (configure fails with gcc 14)
+    # two patches for (1) m4 macro from upstream and (2) pre-generated configure in tarball
+    patch(
+        "https://gitlab.com/libvdwxc/libvdwxc/-/commit/9340f857515c4a2e56d2aa7cf3a21c41ba8559c3.diff",
+        sha256="b9ad695e54a25d7ffa92f783bb0a31d3b421225f97958972e32ba42893844b80",
+        when="@:0.4.0",
+    )
+    patch("fftw-detection.patch", when="@:0.4.0")