Changed the impls argument to be an array name.

Turns out, you can't use preprocessor directives inside macro arguments.
Who'd have thought?

modules/gpu/perf/perf_main.cpp

@@ -44,8 +44,11 @@
 
 using namespace perf;
 
-CV_PERF_TEST_MAIN_WITH_IMPLS(gpu, (
+static const char * impls[] = {
 #ifdef HAVE_CUDA
-                                   "cuda",
+    "cuda",
 #endif
-                                   "plain"), printCudaInfo())
+    "plain"
+};
+
+CV_PERF_TEST_MAIN_WITH_IMPLS(gpu, impls, printCudaInfo())