deps: cherry-pick 6bc4bfe from V8 upstream

Only changes to src/base/debug/stack_trace_posix.cc included

Original commit message:
    Fixes to V8 GN build process on aix platform

    src/base/debug/stack_trace_posix.cc: suppressed unused function warnings
    for functions DemangleSymbols, OutputPointer(in order to compile with
    -Werror flag)

    test/cctest/test-isolate-independent-builtins.cc: corrections to make
    ByteInText test case compatible with aix. (affects aix only)

    Change-Id: I49e45e63545404c77aaed3f51b26557f6f03455e
    Reviewed-on: https://chromium-review.googlesource.com/927484
    Reviewed-by: Jakob Gruber <jgruber@chromium.org>
    Reviewed-by: Michael Achenbach <machenbach@chromium.org>
    Commit-Queue: Jakob Gruber <jgruber@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#52071}

PR-URL: #23958
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Beth Griggs <Bethany.Griggs@uk.ibm.com>
Reviewed-By: George Adams <george.adams@uk.ibm.com>

deps/v8/include/v8-version.h

@@ -11,7 +11,7 @@
 #define V8_MAJOR_VERSION 6
 #define V8_MINOR_VERSION 2
 #define V8_BUILD_NUMBER 414
-#define V8_PATCH_LEVEL 72
+#define V8_PATCH_LEVEL 73
 
 // Use 1 for candidates and 0 otherwise.
 // (Boolean macro values are not supported by all preprocessors.)

deps/v8/src/base/debug/stack_trace_posix.cc

@@ -72,6 +72,7 @@ const char kMangledSymbolPrefix[] = "_Z";
 const char kSymbolCharacters[] =
     "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_";
 
+#if HAVE_EXECINFO_H
 // Demangles C++ symbols in the given text. Example:
 //
 // "out/Debug/base_unittests(_ZN10StackTraceC1Ev+0x20) [0x817778c]"
@@ -81,7 +82,6 @@ void DemangleSymbols(std::string* text) {
   // Note: code in this function is NOT async-signal safe (std::string uses
   // malloc internally).
 
-#if HAVE_EXECINFO_H
 
   std::string::size_type search_from = 0;
   while (search_from < text->size()) {
@@ -117,9 +117,8 @@ void DemangleSymbols(std::string* text) {
       search_from = mangled_start + 2;
     }
   }
-
-#endif  // HAVE_EXECINFO_H
 }
+#endif  // HAVE_EXECINFO_H
 
 class BacktraceOutputHandler {
  public:
@@ -129,6 +128,7 @@ class BacktraceOutputHandler {
   virtual ~BacktraceOutputHandler() {}
 };
 
+#if HAVE_EXECINFO_H
 void OutputPointer(void* pointer, BacktraceOutputHandler* handler) {
   // This should be more than enough to store a 64-bit number in hex:
   // 16 hex digits + 1 for null-terminator.
@@ -139,7 +139,6 @@ void OutputPointer(void* pointer, BacktraceOutputHandler* handler) {
   handler->HandleOutput(buf);
 }
 
-#if HAVE_EXECINFO_H
 void ProcessBacktrace(void* const* trace, size_t size,
                       BacktraceOutputHandler* handler) {
   // NOTE: This code MUST be async-signal safe (it's used by in-process