[PATCH] Avoid -Wconversion warnings when -Wsystem-headers is used

[Jonathan Wakely]

        * include/bits/stl_algobase.h (__lg): Do arithmetic on type int to
        avoid -Wconversion warnings.

Tested powerpc64le-linux, committed to trunk.



commit 81c48e4f55f03edf873fa8ca1111df5920a0e062
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Fri Mar 22 16:27:10 2019 +0000

    Avoid -Wconversion warnings when -Wsystem-headers is used
    
            * include/bits/stl_algobase.h (__lg): Do arithmetic on type int to
            avoid -Wconversion warnings.

diff --git a/libstdc++-v3/include/bits/stl_algobase.h 
b/libstdc++-v3/include/bits/stl_algobase.h
index 2b69e658fe8..3b1139401ee 100644
--- a/libstdc++-v3/include/bits/stl_algobase.h
+++ b/libstdc++-v3/include/bits/stl_algobase.h
@@ -1018,27 +1018,27 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   //  Precondition: __n > 0.
   inline _GLIBCXX_CONSTEXPR int
   __lg(int __n)
-  { return sizeof(int) * __CHAR_BIT__  - 1 - __builtin_clz(__n); }
+  { return (int)sizeof(int) * __CHAR_BIT__  - 1 - __builtin_clz(__n); }
 
   inline _GLIBCXX_CONSTEXPR unsigned
   __lg(unsigned __n)
-  { return sizeof(int) * __CHAR_BIT__  - 1 - __builtin_clz(__n); }
+  { return (int)sizeof(int) * __CHAR_BIT__  - 1 - __builtin_clz(__n); }
 
   inline _GLIBCXX_CONSTEXPR long
   __lg(long __n)
-  { return sizeof(long) * __CHAR_BIT__ - 1 - __builtin_clzl(__n); }
+  { return (int)sizeof(long) * __CHAR_BIT__ - 1 - __builtin_clzl(__n); }
 
   inline _GLIBCXX_CONSTEXPR unsigned long
   __lg(unsigned long __n)
-  { return sizeof(long) * __CHAR_BIT__ - 1 - __builtin_clzl(__n); }
+  { return (int)sizeof(long) * __CHAR_BIT__ - 1 - __builtin_clzl(__n); }
 
   inline _GLIBCXX_CONSTEXPR long long
   __lg(long long __n)
-  { return sizeof(long long) * __CHAR_BIT__ - 1 - __builtin_clzll(__n); }
+  { return (int)sizeof(long long) * __CHAR_BIT__ - 1 - __builtin_clzll(__n); }
 
   inline _GLIBCXX_CONSTEXPR unsigned long long
   __lg(unsigned long long __n)
-  { return sizeof(long long) * __CHAR_BIT__ - 1 - __builtin_clzll(__n); }
+  { return (int)sizeof(long long) * __CHAR_BIT__ - 1 - __builtin_clzll(__n); }
 
 _GLIBCXX_BEGIN_NAMESPACE_ALGO