[libc][math] fix atan2l build failure. (#151413)

Author: bassiounix

libc/src/math/generic/atan2l.cpp

@@ -17,7 +17,7 @@ namespace LIBC_NAMESPACE_DECL {
 LLVM_LIBC_FUNCTION(long double, atan2l, (long double y, long double x)) {
 #if defined(LIBC_TYPES_LONG_DOUBLE_IS_FLOAT64)
   return static_cast<long double>(
-      atan2(static_cast<double>(y), static_cast<double>(x)));
+      math::atan2(static_cast<double>(y), static_cast<double>(x)));
 #else
 #error "Extended precision is not yet supported"
 #endif