mkl: Add a small test program

The MKL pkg-config files often change and are then incorrect for our
paths. pkg-config validation finds some issues, but not incorrect
paths. So, add a small test program to test whether the generated
pkg-config files can actually be used to build a functioning
binary. Hopefully this catches future regressions.

pkgs/development/libraries/science/math/mkl/test/default.nix

@@ -0,0 +1,33 @@
+{ stdenv, pkg-config, mkl }:
+
+stdenv.mkDerivation {
+  pname = "mkl-test";
+  version = mkl.version;
+
+  src = ./.;
+
+  nativeBuildInputs = [ pkg-config ];
+
+  buildInputs = [ mkl ];
+
+  doCheck = true;
+
+  buildPhase = ''
+    # Check regular Nix build.
+    gcc $(pkg-config --cflags --libs mkl-dynamic-ilp64-seq) test.c -o test
+
+    # Clear flags to ensure that we are purely relying on options
+    # provided by pkg-config.
+    NIX_CFLAGS_COMPILE="" \
+    NIX_LDFLAGS="" \
+      gcc $(pkg-config --cflags --libs mkl-dynamic-ilp64-seq) test.c -o test
+  '';
+
+  installPhase = ''
+    touch $out
+  '';
+
+  checkPhase = ''
+    ./test
+  '';
+}