build,deps: enable building V8 as shared library

[refack]

Motivation: Makes linking the node binary faster, which is especially significant when doing a debug build.

The incantation is ./configure ... -- -Dv8_dynamic=true
Files will be in out/[Release\Debug]/lib.target/libv8*.so

/CC @nodejs/build-files

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

[nodejs-github-bot]

@refack build started: https://ci.nodejs.org/blue/organizations/jenkins/node-test-pull-request-lite-pipeline/detail/node-test-pull-request-lite-pipeline/1092/pipeline

[refack]

Blocked by GYP bug/undefined behavior WRT defaults.

[refack]

Fixed, PTAL

[bnoordhuis]

Can you explain (also in the commit log) why this is useful or necessary?

[joyeecheung]

@bnoordhuis To reduce the build time of debug builds

[joyeecheung]

@bnoordhuis (Just realized that you might mean "why not just use ./configure ... -- -Dcomponent= shared_library"...then I guess there really isn't a good reason other than it's more convenient? Does simply setting that flag work though?)

[refack]

Can you explain (also in the commit log) why this is useful or necessary?

As mentioned by @joyeecheung, it makes linking the node binary faster, which is especially significant when doing a debug build. (I'll document this as requested).

"why not just use ./configure ... -- -Dcomponent=shared_library"...

We need to conditionally turn on -fPIC (conditionally because it has a compile time and runtime penalty). Also we have:

node/node.gypi

Lines 261 to 266 in 80225d4

	[ '(OS=="freebsd" or OS=="linux") and node_shared=="false"'
	' and force_load=="true" and v8_dynamic!="true"', {
	'ldflags': [ '-Wl,-z,noexecstack',
	'-Wl,--whole-archive <(v8_base)',
	'-Wl,--no-whole-archive' ]
	}],

I am considering adding it as a flag to configure.py, that will come with some docu.

BTW: There's still is a bug, since now we need to also compile ICU with -fPIC, since now it's a direct dependency of V8.

[bnoordhuis]

We need to conditionally turn on -fPIC

You can do that by guarding on ['component=="shared_library"', ...], it doesn't need a new variable.

[Trott]

What is this blocked on?

[refack]

Making it simpler (remove the new flag, and just guard for special cases using the existing V8 flag component=="shared_library")