[Libomptarget] Disable AMDGPU complex math test after recent patch

Summary:
The recent patch added `-nogpulib` to make these tests only pick up what
was intentionally put into them. This had the effect of removing the
dependency on the ROCm device libs which are needed for math. This test
disables the complex math test, which is the only one that needed it,
for the time being. In the future we will implement these and provide it
via the GPU `libm` and pass it in the same way as the GPU `libc`.

Author: jhuber6

openmp/libomptarget/test/offloading/std_complex_arithmetic.cpp

@@ -3,6 +3,10 @@
 // RUN: %libomptarget-compilexx-generic -O3 -ffast-math && \
 // RUN:   %libomptarget-run-generic
 
+// FIXME: This fails to link due to missing math symbols. We should provide the
+//        needed math functions in the GPU `libm` and require the GPU C library.
+// UNSUPPORTED: amdgcn-amd-amdhsa
+
 #include <cassert>
 #include <complex>
 #include <iostream>