Fix warning with -Wsign-compare -Wsystem-headers

	* include/tr1/legendre_function.tcc (__sph_legendre): Avoid warning
	about signed/unsigned comparison.

From-SVN: r263596

libstdc++-v3/ChangeLog

 2018-08-16  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/tr1/legendre_function.tcc (__sph_legendre): Avoid warning
+	about signed/unsigned comparison.
+
 	* include/std/ostream (basic_ostream::sentry::~sentry): Suppress
 	deprecation warnings for using uncaught_exception().
 

libstdc++-v3/include/tr1/legendre_function.tcc

@@ -284,7 +284,7 @@ namespace tr1
               _Tp __y_lm = _Tp(0);
 
               // Compute Y_l^m, l > m+1, upward recursion on l.
-              for ( int __ll = __m + 2; __ll <= __l; ++__ll)
+              for (unsigned int __ll = __m + 2; __ll <= __l; ++__ll)
                 {
                   const _Tp __rat1 = _Tp(__ll - __m) / _Tp(__ll + __m);
                   const _Tp __rat2 = _Tp(__ll - __m - 1) / _Tp(__ll + __m - 1);