Fix numeric_limits<XXX>::is_modulo for signed arithmetic types. We were reporting true, for all arithmetic types, which is incorrect. Fix the tests which were wrong, too. This fixes PR#20158.

llvm-svn: 214371
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 6a577a819f5b942e3a7f6212c2f0059e9fef8ad3
diff --git a/include/limits b/include/limits
index 2216966..1acf03e 100644
--- a/include/limits
+++ b/include/limits
@@ -235,7 +235,7 @@
 
     static _LIBCPP_CONSTEXPR const bool is_iec559 = false;
     static _LIBCPP_CONSTEXPR const bool is_bounded = true;
-    static _LIBCPP_CONSTEXPR const bool is_modulo = true;
+    static _LIBCPP_CONSTEXPR const bool is_modulo = !_VSTD::is_signed<_Tp>::value;
 
 #if __i386__ || __x86_64__
     static _LIBCPP_CONSTEXPR const bool traps = true;