add smoke test

Author: bassiounix

libc/test/shared/CMakeLists.txt

@@ -21,4 +21,5 @@ add_fp_unittest(
     libc.src.__support.math.ldexpf
     libc.src.__support.math.ldexpf128
     libc.src.__support.math.ldexpf16
+    libc.src.__support.math.acosf16
 )

libc/test/shared/shared_math_test.cpp

@@ -25,6 +25,8 @@ TEST(LlvmLibcSharedMathTest, AllFloat16) {
   EXPECT_FP_EQ_ALL_ROUNDING(0.75f16,
                             LIBC_NAMESPACE::shared::frexpf16(24.0f, &exponent));
   EXPECT_EQ(exponent, 5);
+
+  EXPECT_FP_EQ(0x1.921fb6p+0f16, LIBC_NAMESPACE::shared::acosf16(0.0f16));
 }
 
 #endif