Refactor the process of choosing validators.

src/trusted/service_runtime/service_runtime.gyp

Index: src/trusted/service_runtime/service_runtime.gyp
diff --git a/src/trusted/service_runtime/service_runtime.gyp b/src/trusted/service_runtime/service_runtime.gyp
index ffc40df4ae15bb920d34df5796e842cae1434e73..6e1a14e0fe643603fc9ad16fc179fb7f2fc2cd35 100644
--- a/src/trusted/service_runtime/service_runtime.gyp
+++ b/src/trusted/service_runtime/service_runtime.gyp
@@ -65,6 +65,7 @@
           'sel_qualify.c',
           'sel_validate_image.c',
           'thread_suspension_common.c',
+          '<(DEPTH)/native_client/src/trusted/validator/validator_init.c',

[Mark Seaborn, 2012/06/14 20:11:56]

This is messy.  service_runtime.gyp shouldn't be building something from
src/trusted/validator.  Also it's not consistent with what you've done in the
Scons build.

[pasko-google - do not use, 2012/06/17 14:46:45]

I agree this looks different than inclusion of other sources to "sel".

In the scons build I created a library out of one file and made it depend on the
rest of the platform-dependent validator libraries (that become conditional in
GYP depending on nacl_standalone). I did not find a way to do it in GYP without
creating one more GYP file, which I considered overkill.

I'd appreciate if your GYP expertise produced an elegant variant of this.

[Mark Seaborn, 2012/06/20 20:02:26]

Creating a new, arch-neutral Gyp file, src/validator/validator.gyp, seems like
the right thing to do.

Your change is creating a single entry point for getting the validator, and it
would make sense to also have a single build-time 'entry point' for library
dependencies.

src/validator/validator.gyp only needs to contain validator_init.c for now. 
(Cleaning up the validator dependencies in
src/trusted/service_runtime/service_runtime.gyp and
src/trusted/service_runtime/arch/x86/service_runtime_x86.gyp can be left to
later changes.)

[pasko-google - do not use, 2012/06/21 15:24:18]

I added the trusted/validator/validator.gyp.
Though I do not fully understand what we should clean up in validator
dependencies. What is wrong with current dependencies between libraries besides
the unclean conditional linking with nacl_standalone? 

         ],
         'include_dirs': [
           # For generated header files from the x86-64 validator,