Improvements to GYP build

This updates the GYP build for the processor component (on windows).
- adds/removes references to files which were added or removed from the
  repository
- includes build/common.gypi in the gyp files: needed to correctly
  detect the OS (I think, the generated MSVC solutions were broken
  without it)
- conditionally compiles code platform-specific code for the given
  platform

After this minidump processor nearly compiles with VS2013: the generated
project is correct, but some files still have compilation errors.

Disclaimer: I have not tested the GYP changes on non-windows platform,
as there does not seem to be anyone using it there.

BUG=
R=mark@chromium.org

Review URL: https://codereview.chromium.org/1643633004 .

src/third_party/libdisasm/libdisasm.gyp

@@ -27,6 +27,9 @@
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 {
+  'includes': [
+    '../../build/common.gypi',
+  ],
   'targets': [
     {
       'target_name': 'libdisasm',