testsuite: require c99 runtime for trigonometric optimisation tests

A number of optimisation that simplify trigonometric expressions are only
performed when the compiler knows the target has a C99 libm available.
Since targets like *-elf may not have such a libm, a C99 runtime requirement
is added to these tests.

2020-08-19  Pat Bernardi  <bernardi@adacore.com>

gcc/testsuite/ChangeLog

	* gcc.dg/sinatan-2.c: Add dg-require-effective-target c99_runtime.
	* gcc.dg/sinhovercosh-1.c: Likewise.
	* gcc.dg/tanhbysinh.c: Likewise.

gcc/testsuite/gcc.dg/sinatan-2.c

@@ -1,5 +1,6 @@
 /* { dg-do compile } */
 /* { dg-options "-Ofast -fdump-tree-optimized" } */
+/* { dg-require-effective-target c99_runtime } */
 
 extern float sinf (float);
 extern float cosf (float);

gcc/testsuite/gcc.dg/sinhovercosh-1.c

@@ -1,5 +1,6 @@
 /* { dg-do compile } */
 /* { dg-options "-Ofast -fdump-tree-optimized" } */
+/* { dg-require-effective-target c99_runtime } */
 
 extern float sinhf (float);
 extern float coshf (float);

gcc/testsuite/gcc.dg/tanhbysinh.c

@@ -1,5 +1,6 @@
 /* { dg-do compile } */
 /* { dg-options "-Ofast -fdump-tree-optimized" } */
+/* { dg-require-effective-target c99_runtime } */
 
 extern float sinhf (float);
 extern float tanhf (float);
@@ -37,4 +38,4 @@ tanhbysinhl_ (long double x)
 /* {dg-final { scan-tree-dump-not "tanhl " "optimized" }} */
 /* { dg-final { scan-tree-dump "cosh " "optimized" } } */
 /* { dg-final { scan-tree-dump "coshf " "optimized" } } */
-/* { dg-final { scan-tree-dump "coshl " "optimized" } } */
+/* { dg-final { scan-tree-dump "coshl " "optimized" } } */