Modular build: Disable scons_compile_tests since it failed on a from-scratch build
Modular build: Disable scons_compile_tests since it failed on a from-scratch build

Fixes breakage introduced in r3279.

BUG=http://code.google.com/p/nativeclient/issues/detail?id=863
TEST="python build.py -b" after deleting out/headers*, which contained
  stale files that the build scripts do not yet correctly update
  incrementally.

Review URL: http://codereview.chromium.org/3433002

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@3285 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client