Add clang < 7 to conditions

absl/strings/charconv.cc

@@ -339,13 +339,15 @@ template <typename FloatType>
 bool HandleEdgeCase(const strings_internal::ParsedFloat& input, bool negative,
                     FloatType* value) {
   if (input.type == strings_internal::FloatType::kNan) {
-    // A bug in gcc would cause the compiler to optimize away the buffer 
-    // we are building below.  Declaring the buffer volatile avoids the
-    // issue, and has no measurable performance impact in microbenchmarks.
+    // A bug in both clang < 7 and gcc would cause the compiler to optimize
+    // away the buffer we are building below.  Declaring the buffer volatile
+    // avoids the issue, and has no measurable performance impact in
+    // microbenchmarks.
     //
+    // https://bugs.llvm.org/show_bug.cgi?id=37778
     // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86113
     constexpr ptrdiff_t kNanBufferSize = 128;
-#ifdef __GNUC__
+#if defined(__GNUC__) || (defined(__clang__) && __clang_major__ < 7)
     volatile char n_char_sequence[kNanBufferSize];
 #else
     char n_char_sequence[kNanBufferSize];