ninja: Change the default target from 'build everything' to 'build target "all"'.

ninja: Change the default target from 'build everything' to 'build target "all"'.

'all' are all targets transitively referenced by all.gyp.  For example:

all.gyp:
  targets: [
    {
      'target_name': 'main_target',
      'dependencies': [
        'dep.gyp:target1',
      ],
    },
  ]

dep.gyp:
  targets: [
    { 'target_name': 'target1' },
    { 'target_name': 'target2' },
  ]

Here, 'all' does include target1 from dep.gyp, but not target2.
The generator still writes a ninja file for target2, and it can
be built with 'ninja target2', but just 'ninja' will no longer
build it.

BUG=127952
TEST=Running just `ninja -C out/Release` doesn't produce errors.
Committed: https://code.google.com/p/gyp/source/detail?r=1380

[Nico, 2012-05-16 21:00:38]

I agree it's weird that 'all' doesn't include all targets, but that's not
something new in this CL.

[scottmg, 2012-05-16 21:06:39]

lgtm

we could probably test that? but not too worried about it since it's sort of
"ui".

[Nico, 2012-05-16 21:08:35]

On 2012/05/16 21:06:39, scottmg wrote:
> lgtm
> 
> we could probably test that? but not too worried about it since it's sort of
> "ui".

agreed