[lldb/Test] Use lit's capabilities to skip lldb-repro tests.

This allows us to skip the reproducer tests themselves as a whole as
well as individual tests with the UNSUPPORTED keyword.

lldb/test/Shell/Process/TestEnvironment.test

@@ -1,4 +1,5 @@
 UNSUPPORTED: system-windows
+UNSUPPORTED: lldb-repro
 
 The double quotes around "BAR" ensure we don't match the command.
 

lldb/test/Shell/Quit/TestQuitExitCode-30.test

@@ -1,3 +1,4 @@
 # UNSUPPORTED: system-windows
+# UNSUPPORTED: lldb-repro
 # RUN: %python %S/expect_exit_code.py 226 %lldb -b -s %s
 q -30

lldb/test/Shell/Quit/TestQuitExitCode30.test

@@ -1,3 +1,4 @@
 # UNSUPPORTED: system-windows
+# UNSUPPORTED: lldb-repro
 # RUN: %python %S/expect_exit_code.py 30  %lldb -b -s %s
 q 30

lldb/test/Shell/Quit/TestQuitExitCodeHexA.test

@@ -1,3 +1,4 @@
 # UNSUPPORTED: system-windows
+# UNSUPPORTED: lldb-repro
 # RUN: %python %S/expect_exit_code.py 10 %lldb -b -s %s
 q 0xA

lldb/test/Shell/Reproducer/lit.local.cfg

@@ -6,5 +6,5 @@ if 'LLVM_DISABLE_CRASH_REPORT' in config.environment:
 if 'LLDB_CAPTURE_REPRODUCER' in config.environment:
   del config.environment['LLDB_CAPTURE_REPRODUCER']
 
-if hasattr(config, 'skip_reproducer_test') and config.skip_reproducer_test:
+if 'lldb-repro' in config.available_features:
   config.unsupported = True

lldb/test/Shell/lit.cfg.py

@@ -48,7 +48,7 @@ if 'LLDB_CAPTURE_REPRODUCER' in os.environ:
 # just captured reproducer.
 lldb_repro_mode = lit_config.params.get('lldb-run-with-repro', None)
 if lldb_repro_mode:
-  config.skip_reproducer_test = True
+  config.available_features.add('lldb-repro')
   lit_config.note("Running Shell test with lldb-repo in {} mode.".format(lldb_repro_mode))
   toolchain.use_lldb_repro_substitutions(config, lldb_repro_mode)