[regexp] Add missing const qualifier

This is patching 560f2d8b for a
failing android-binary-size bot, see
https://chromium-review.googlesource.com/c/chromium/src/+/2110413

TBR=rmcilroy@chromium.org

Bug: chromium:747064
Change-Id: I37c5484afa427420d7a4614300556f7a5e99b21d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2111211Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66802}

src/regexp/regexp-error.cc

@@ -7,7 +7,7 @@
 namespace v8 {
 namespace internal {
 
-const char* kRegExpErrorStrings[] = {
+const char* const kRegExpErrorStrings[] = {
 #define TEMPLATE(NAME, STRING) STRING,
     REGEXP_ERROR_MESSAGES(TEMPLATE)
 #undef TEMPLATE