[clang][AIX] Strip unknown environment component for per target runtime directory (#140850)

Previously, when the triple is `powerpc-ibm-aix-unknown`, the driver
fails to find subdirectory `lib/powerpc-ibm-aix`.

This ensures the correct runtime path is found if the triple has the
-unknown environment component attached.

Author: jakeegan

clang/lib/Driver/ToolChain.cpp

@@ -933,6 +933,15 @@ ToolChain::getTargetSubDirPath(StringRef BaseDir) const {
   if (auto Path = getPathForTriple(T))
     return *Path;
 
+  if (T.isOSAIX() && T.getEnvironment() == Triple::UnknownEnvironment) {
+    // Strip unknown environment from the triple.
+    const llvm::Triple AIXTriple(
+        llvm::Triple(T.getArchName(), T.getVendorName(),
+                     llvm::Triple::getOSTypeName(T.getOS())));
+    if (auto Path = getPathForTriple(AIXTriple))
+      return *Path;
+  }
+
   if (T.isOSzOS() &&
       (!T.getOSVersion().empty() || !T.getEnvironmentVersion().empty())) {
     // Build the triple without version information

clang/test/Driver/aix-print-runtime-dir.c

@@ -16,6 +16,16 @@
 // RUN:        -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir\
 // RUN:      | FileCheck --check-prefix=PRINT-RUNTIME-DIR64-PER-TARGET %s
 
+// RUN: %clang -print-runtime-dir --target=powerpc-ibm-aix-unknown \
+// RUN:        -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
+// RUN:      | FileCheck --check-prefix=PRINT-RUNTIME-DIR32-UNKNOWN-ENV %s
+
+// RUN: %clang -print-runtime-dir --target=powerpc64-ibm-aix-unknown \
+// RUN:        -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
+// RUN:      | FileCheck --check-prefix=PRINT-RUNTIME-DIR64-UNKNOWN-ENV %s 
+
 // PRINT-RUNTIME-DIR: lib{{/|\\}}aix{{$}}
 // PRINT-RUNTIME-DIR32-PER-TARGET: lib{{/|\\}}powerpc-ibm-aix{{$}}
 // PRINT-RUNTIME-DIR64-PER-TARGET: lib{{/|\\}}powerpc64-ibm-aix{{$}}
+// PRINT-RUNTIME-DIR32-UNKNOWN-ENV: lib{{/|\\}}powerpc-ibm-aix
+// PRINT-RUNTIME-DIR64-UNKNOWN-ENV: lib{{/|\\}}powerpc64-ibm-aix