[PATCH] Fix warning with -Wsign-compare -Wsystem-headers in __sph_legendre

[Jonathan Wakely]

Ed, I'm checking this in as it looks correct anyway, quite apart from
the fact it fixes a warning, but could you please double check it?

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

Tested x86_64-linux, committed to trunk.



commit 67aca02fcfb8cde961480ebb1a2d19d1439d2e98
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Thu Aug 16 17:57:58 2018 +0100

    Fix warning with -Wsign-compare -Wsystem-headers
    
            * include/tr1/legendre_function.tcc (__sph_legendre): Avoid warning
            about signed/unsigned comparison.

diff --git a/libstdc++-v3/include/tr1/legendre_function.tcc 
b/libstdc++-v3/include/tr1/legendre_function.tcc
index 85ca7969f5b..e75414c5296 100644
--- a/libstdc++-v3/include/tr1/legendre_function.tcc
+++ b/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);