[ADT/STLExtras.h] - Add llvm::is_sorted wrapper and update callers.

It can be used to avoid passing the begin and end of a range.
This makes the code shorter and it is consistent with another
wrappers we already have.

Differential revision: https://reviews.llvm.org/D78016
diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index fb0c8b3..812fdc6 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -5352,7 +5352,7 @@
 
 #ifndef NDEBUG
   if (!MapProvenSorted) {
-    assert(std::is_sorted(std::begin(IntrinsicMap), std::end(IntrinsicMap)));
+    assert(llvm::is_sorted(IntrinsicMap));
     MapProvenSorted = true;
   }
 #endif