libstdc++: testsuite: require cmath for nexttowardl

nexttowardl is only expected to be available with C99 math, but
20_util/to_chars/long_double.cc uses it unconditionally.

State the cmath requirement in the test.

for  libstdc++-v3/ChangeLog

	* testsuite/20_util/to_chars/long_double.cc: Require cmath.

diff --git a/libstdc++-v3/testsuite/20_util/to_chars/long_double.cc b/libstdc++-v3/testsuite/20_util/to_chars/long_double.cc
index 94b5b5967d374965edb97fd406dfc4e2de5f4c1a..0b1c2c2936fdc07c6920a124e9cec5227c396c13 100644 (file)
--- a/libstdc++-v3/testsuite/20_util/to_chars/long_double.cc
+++ b/libstdc++-v3/testsuite/20_util/to_chars/long_double.cc
@@ -36,6 +36,7 @@
 
 // { dg-require-effective-target ieee_floats }
 // { dg-require-effective-target size32plus }
+// { dg-require-cmath "" }
 
 #include <charconv>