Use a shared module cache directory for LLDB.

[aprantl]

Summary

This saves about 3 redundant gigabytes from the Objective-C test build
directories. Tests that must do unsavory things with the LLDB clang
module cache, already specify a per-test module cache in their .py
test instructions.

rdar://problem/36002081

[JDevlieghere]

LGTM

[davide]

lgtm

lit/lit.cfg.py

llvm_config.feature_config(
     [('--assertion-mode', {'ON': 'asserts'}),
      ('--build-mode', {'DEBUG': 'debug'}),
      ('--targets-built', calculate_arch_features)
      ])
 
 # Clean the module caches in the test build directory.  This is
 # necessary in an incremental build whenever clang changes underneath,
 # so doing it once per lit.py invocation is close enough.
-for i in ['module-cache-clang']:
+for i in ['module-cache-clang', 'module-cache-lldb']:
     cachedir = os.path.join(config.llvm_obj_root, 'lldb-test-build.noindex', i)
     if os.path.isdir(cachedir):
         print("Deleting module cache at %s."%cachedir)
         shutil.rmtree(cachedir)

packages/Python/lldbsuite/test/lldbtest.py

class TestBase(Base):
     def setUp(self):
         #import traceback
         # traceback.print_stack()
 
         # Works with the test driver to conditionally skip tests via
         # decorators.
         Base.setUp(self)
 
-        # Set the clang modules cache path.
-        mod_cache = os.path.join(self.getBuildDir(), "module-cache-lldb")
+        # Set the clang modules cache path used by LLDB.
+        mod_cache = os.path.join(os.path.join(os.environ["LLDB_BUILD"],
+                                              "module-cache-lldb"))
         self.runCmd('settings set symbols.clang-modules-cache-path "%s"'
                     % mod_cache)
 
         # Disable Spotlight lookup. The testsuite creates
         # different binaries with the same UUID, because they only
         # differ in the debug info, which is not being hashed.
         self.runCmd('settings set symbols.enable-external-lookup false')