Placate unused variable warnings uncovered by improvements to clang's -Wunused-variable

llvm-svn: 315809
diff --git a/libcxx/test/std/depr/depr.c.headers/tgmath_h.pass.cpp b/libcxx/test/std/depr/depr.c.headers/tgmath_h.pass.cpp
index 965a8de..91727b6 100644
--- a/libcxx/test/std/depr/depr.c.headers/tgmath_h.pass.cpp
+++ b/libcxx/test/std/depr/depr.c.headers/tgmath_h.pass.cpp
@@ -14,6 +14,7 @@
 int main()
 {
     std::complex<double> cd;
+    (void)cd;
     double x = sin(1.0);
     (void)x; // to placate scan-build
 }