[AIX] Add system-aix to lit config file

[ShuhongL]

Summary

This is a complementary patch to D82100 since the aix builbot is still running the unsupported test shtest-format-argv0. Add system-aix to the sub llvm-lit config.

[hubert.reinterpretcast]

LGTM.

llvm/utils/lit/lit/llvm/config.py

def __init__(self, lit_config, config):
         if platform.system() == 'Darwin':
             # FIXME: lld uses the first, other projects use the second.
             # We should standardize on the former.
             features.add('system-linker-mach-o')
             features.add('system-darwin')
         elif platform.system() == 'Windows':
             # For tests that require Windows to run.
             features.add('system-windows')
-        elif platform.system() == "Linux":
+        elif platform.system() == 'Linux':
             features.add('system-linux')
         elif platform.system() in ['FreeBSD']:
             features.add('system-freebsd')
-        elif platform.system() == "NetBSD":
+        elif platform.system() == 'NetBSD':
             features.add('system-netbsd')
+        elif platform.system() == 'AIX':
+            features.add('system-aix')
 
         # Native compilation: host arch == default triple arch
         # Both of these values should probably be in every site config (e.g. as
         # part of the standard header.  But currently they aren't)
         host_triple = getattr(config, 'host_triple', None)
         target_triple = getattr(config, 'target_triple', None)
         if host_triple and host_triple == target_triple:
             features.add('native')

llvm/utils/lit/tests/lit.cfg

 
 # When running the lit tests standalone, we want to define the same features
 # that the llvm_config defines. This means that the 'system-windows' feature
 # (and any others) need to match the names in llvm_config for consistency
 if not llvm_config:
   if sys.platform.startswith('win') or sys.platform.startswith('cygwin'):
     config.available_features.add('system-windows')
   if platform.system() == 'AIX':
-    config.available_features.add('aix')
+    config.available_features.add('system-aix')
 
 # For each of lit's internal shell commands ('env', 'cd', 'diff', etc.), put
 # a fake command that always fails at the start of PATH.  This helps us check
 # that we always use lit's internal version rather than some external version
 # that might not be present or behave correctly on all platforms.  Don't do
 # this for 'echo' because an external version is used when it appears in a
 # pipeline.  Don't do this for ':' because it doesn't appear to be a valid file
 # name under Windows.
 test_bin = os.path.join(os.path.dirname(__file__), 'Inputs', 'fake-externals')
 config.environment['PATH'] = os.path.pathsep.join((test_bin,
                                                    config.environment['PATH']))

llvm/utils/lit/tests/shtest-format-argv0.py

 # Check that we route argv[0] as it was written, instead of the resolved
 # path. This is important for some tools, in particular '[' which at least on OS
 # X only recognizes that it is in '['-mode when its argv[0] is exactly
 # '['. Otherwise it will refuse to accept the trailing closing bracket.
 #
 # This test is not supported on AIX since `[` is only available as a shell builtin
 # and is not installed under PATH by default.
-# UNSUPPORTED: aix
+# UNSUPPORTED: system-aix
 #
 # RUN: %{lit} -j 1 -v %{inputs}/shtest-format-argv0 | FileCheck %s
 
 # CHECK: -- Testing:
 # CHECK: PASS: shtest-format-argv0 :: argv0.txt