Fix complex.csqrtf test and add a trivial sincosl test.

sincos and sincosf are being tested more thoroughly with a table of data,
but there's nothing equivalent for sincosl.

Test: ran the tests, obviously.
Change-Id: I5b4b22b73cad9b0030549de2e2ed2a0e38648806
diff --git a/tests/math_test.cpp b/tests/math_test.cpp
index c805cc2..6c7dffb 100644
--- a/tests/math_test.cpp
+++ b/tests/math_test.cpp
@@ -385,6 +385,27 @@
   ASSERT_DOUBLE_EQ(0.0L, sinl(0.0L));
 }
 
+TEST(math, sincos) {
+  double s, c;
+  sincos(0.0, &s, &c);
+  ASSERT_DOUBLE_EQ(0.0, s);
+  ASSERT_DOUBLE_EQ(1.0, c);
+}
+
+TEST(math, sincosf) {
+  float s, c;
+  sincosf(0.0f, &s, &c);
+  ASSERT_FLOAT_EQ(0.0f, s);
+  ASSERT_FLOAT_EQ(1.0f, c);
+}
+
+TEST(math, sincosl) {
+  long double s, c;
+  sincosl(0.0L, &s, &c);
+  ASSERT_DOUBLE_EQ(0.0L, s);
+  ASSERT_DOUBLE_EQ(1.0L, c);
+}
+
 TEST(math, tan) {
   ASSERT_DOUBLE_EQ(0.0, tan(0.0));
 }