Disable buffer initialization in hot function

Bug: chromium:1055317, chromium:1055312, chromium:977230
Change-Id: I877bc1547e21c95f4b82b3741949e88e22fc006b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2077222
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66489}

src/numbers/conversions.cc

@@ -583,7 +583,8 @@ double InternalStringToDouble(Iterator current, EndMark end, int flags,
 
   // The longest form of simplified number is: "-<significant digits>'.1eXXX\0".
   const int kBufferSize = kMaxSignificantDigits + 10;
-  char buffer[kBufferSize];  // NOLINT: size is known at compile time.
+  // Avoid slowdown in js-perf-test/Numbers. See crbug.com/1055317.
+  V8_STACK_UNINITIALIZED char buffer[kBufferSize];
   int buffer_pos = 0;
 
   // Exponent will be adjusted if insignificant digits of the integer part