[gcc(refs/users/meissner/heads/work005)] libstdc++: Fix warnings with -Wsystem-headers

[gcc(refs/users/meissner/heads/work005)] libstdc++: Fix warnings with -Wsystem-headers

[Michael Meissner]

https://gcc.gnu.org/g:25920dd18ad12ea501309b1487366e22f35db631

commit 25920dd18ad12ea501309b1487366e22f35db631
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Jun 24 12:34:17 2020 +0100

    libstdc++: Fix warnings with -Wsystem-headers
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/stl_algobase.h (__find_if): Add FALLTHRU markers.
            * include/std/charconv (__detail::__to_chars): Avoid
            -Wsign-compare warning.

Diff:
---
 libstdc++-v3/include/bits/stl_algobase.h | 3 +++
 libstdc++-v3/include/std/charconv        | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/bits/stl_algobase.h b/libstdc++-v3/include/bits/stl_algobase.h
index 4fc8850d707..ff5b4505a08 100644
--- a/libstdc++-v3/include/bits/stl_algobase.h
+++ b/libstdc++-v3/include/bits/stl_algobase.h
@@ -2092,14 +2092,17 @@ _GLIBCXX_END_NAMESPACE_ALGO
 	  if (__pred(__first))
 	    return __first;
 	  ++__first;
+	  // FALLTHRU
 	case 2:
 	  if (__pred(__first))
 	    return __first;
 	  ++__first;
+	  // FALLTHRU
 	case 1:
 	  if (__pred(__first))
 	    return __first;
 	  ++__first;
+	  // FALLTHRU
 	case 0:
 	default:
 	  return __last;
diff --git a/libstdc++-v3/include/std/charconv b/libstdc++-v3/include/std/charconv
index 77a72d40dd0..8fbf64058ee 100644
--- a/libstdc++-v3/include/std/charconv
+++ b/libstdc++-v3/include/std/charconv
@@ -142,7 +142,7 @@ namespace __detail
 	'u', 'v', 'w', 'x', 'y', 'z'
       };
 
-      while (__val >= __base)
+      while (__val >= (unsigned)__base)
 	{
 	  auto const __quo = __val / __base;
 	  auto const __rem = __val % __base;