Start stitching GYP-generated files into the Linux build:...

Start stitching GYP-generated files into the Linux build:
* Add a GYP=1 command-line variable to use the gyp-generated files
  (which are generated side-by-side until everything's okay enough
  to cut over for real).

* Rearrange existing *.scons files to match the layout of the
  gyp-generated ones, so the transition will be easier:
  * base.scons (the wrapping logic that calls the other *.scons files)
    => base_sln.scons
  * base_lib.scons (the library itself)
    => base.scons (matching the gyp target generation)
  * gfx/base_gfx.scons
    => base_gfx.scons (with necessary prepending of "gfx/" to path names)

build/SConscript.main fixes:
* Use an internal ${_GYP} infix variable to select the right flavor
  of *.scons file (multiple places)
* When building with GYP=1, only load the one component *_sln_gyp.scons
  file, because gyp has already created it with knowledge of all the
  right dependent *_gyp.scons files to load.

Linux gyp build fixes:
* Add -32 to $ASFLAGS for generating a 32-bit libicudata.a from the
  now-checked in .s.
* Add -Wno-unused and -Wno-unused-function to skia.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=10759

[sgk, 2009-02-26 20:14:41]

Sending this out for review while I work on a corresponding prerequisite update
for icu38.

The basic idea here is similar to the other platforms:   base.scons (e.g.) is
the current, checked-in  file, and base_gyp.scons is the gyp-generated one.

The change to implement this is a little more complex than it might otherwise be
because we *had* been using the name "base.scons" to be the wrapper that called
all the target *.scons files, and "base_lib.scons" was the file that actually
had the configuration to build the library itself.  This CL undoes that bit so
the checked-in file names correspond to the gyp-generated ones to which we'll be
transitioning.

This is all controlled by a GYP=1 variable on the command line, which just
switches between using the "_gyp" infix or not on the .scons file names it
includes in the build.

[Mark Mentovai, 2009-02-26 20:33:56]

This LGTM, but I'm not sure I understand the approach entirely.  It seems like
you intend for the gyp-based scons build to use some gyp-generated files and
some hand-maintained files?

[tony, 2009-02-27 01:34:16]

base.scons seems to be missing from this patch.

Will scons be generating the .sln files on windows?  If not, it seems weird that
base.scons is being renamed to base_sln.scons since that code won't be used.  If
scons is for the linux build, I imagine something like base_main.scons would be
more appropriate.

[sgk, 2009-02-27 19:07:37]

I think base.scons might not be showing up here because this CL is
simultaneously moving the old base.scons to base_main.scons, and moving the old
base_lib.scons to base.scons, with no content changes.  This ends up looking
like this in my 'svn st' output:

A  +   base_main.scons
R  +   base.scons
A  +   base_gfx.scons
D      gfx/base_gfx.scons
D      base_lib.scons