[PATCH] Avoid warnings in <charconv>

[Jonathan Wakely]

	* include/bits/charconv.h (__to_chars_len): Avoid -Wsign-compare
	warnings.

Tested x86_64-linux. Committed to trunk.
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commit 0839fa95cf5775f0022b35cda01bb0d6c27ca08a
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Oct 11 16:10:24 2019 +0100

    Avoid warnings in <charconv>
    
            * include/bits/charconv.h (__to_chars_len): Avoid -Wsign-compare
            warnings.

diff --git a/libstdc++-v3/include/bits/charconv.h b/libstdc++-v3/include/bits/charconv.h
index a5b6be567bc..7c0922fec21 100644
--- a/libstdc++-v3/include/bits/charconv.h
+++ b/libstdc++-v3/include/bits/charconv.h
@@ -50,16 +50,16 @@ namespace __detail
       static_assert(is_unsigned<_Tp>::value, "implementation bug");
 
       unsigned __n = 1;
-      const int __b2 = __base  * __base;
-      const int __b3 = __b2 * __base;
-      const int __b4 = __b3 * __base;
+      const unsigned __b2 = __base  * __base;
+      const unsigned __b3 = __b2 * __base;
+      const unsigned long __b4 = __b3 * __base;
       for (;;)
 	{
-	  if (__value < __base) return __n;
+	  if (__value < (unsigned)__base) return __n;
 	  if (__value < __b2) return __n + 1;
 	  if (__value < __b3) return __n + 2;
 	  if (__value < __b4) return __n + 3;
-	  __value /= (unsigned)__b4;
+	  __value /= __b4;
 	  __n += 4;
 	}
     }