build: add V8 embedder version string

After this commit, `process.versions.v8` will look like:
"6.0.287.53-node.0".
The goal is that everytime we apply a non-official patch to `deps/v8`,
we increment our own number instead of V8's patch level.
This number must be set back to 0 after major V8 updates.

Closes: nodejs#15698

common.gypi

@@ -25,6 +25,10 @@
     # Default to -O0 for debug builds.
     'v8_optimized_debug%': 0,
 
+    # Reset this number to 0 on major V8 upgrades.
+    # Increment by one for each non-official patch applied to deps/v8.
+    'v8_embedder_string': '-node.0',
+
     # Enable disassembler for `--print-code` v8 options
     'v8_enable_disassembler': 1,
 

doc/api/process.md

@@ -1790,6 +1790,9 @@ changes:
   - version: v4.2.0
     pr-url: https://github.com/nodejs/node/pull/3102
     description: The `icu` property is now supported.
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/15785
+    description: The `v8` property now includes a Node.js specific suffix.
 -->
 
 * {Object}
@@ -1810,7 +1813,7 @@ Will generate an object similar to:
 {
   http_parser: '2.3.0',
   node: '1.1.1',
-  v8: '4.1.0.14',
+  v8: '6.1.534.42-node.0',
   uv: '1.3.0',
   zlib: '1.2.8',
   ares: '1.10.0-DEV',

lib/internal/v8_prof_polyfill.js

@@ -82,14 +82,16 @@ function readline() {
 }
 
 function versionCheck() {
-  // v8-version looks like "v8-version,$major,$minor,$build,$patch,$candidate"
-  // whereas process.versions.v8 is either "$major.$minor.$build" or
-  // "$major.$minor.$build.$patch".
+  // v8-version looks like
+  // "v8-version,$major,$minor,$build,$patch[,$embedder],$candidate"
+  // whereas process.versions.v8 is either "$major.$minor.$build-$embedder" or
+  // "$major.$minor.$build.$patch-$embedder".
   var firstLine = readline();
   line = firstLine + '\n' + line;
   firstLine = firstLine.split(',');
-  const curVer = process.versions.v8.split('.');
-  if (firstLine.length !== 6 && firstLine[0] !== 'v8-version') {
+  const curVer = process.versions.v8.split(/\.-/);
+  if (firstLine.length !== 6 && firstLine.length !== 7 ||
+      firstLine[0] !== 'v8-version') {
     console.log('Unable to read v8-version from log file.');
     return;
   }

test/parallel/test-process-versions.js

@@ -29,7 +29,7 @@ assert(commonTemplate.test(process.versions.node));
 assert(commonTemplate.test(process.versions.uv));
 assert(commonTemplate.test(process.versions.zlib));
 
-assert(/^\d+\.\d+\.\d+(?:\.\d+)?(?: \(candidate\))?$/
+assert(/^\d+\.\d+\.\d+(?:\.\d+)?-node\.\d+(?: \(candidate\))?$/
   .test(process.versions.v8));
 assert(/^\d+$/.test(process.versions.modules));