[PowerPC][clang] Fix triple constructor ambiguity causing "unknown" target triple on AIX (#147488)

PR #145685 introduced constructor overload ambiguity in the Triple
class, causing `updateTripleOSVersion()` to construct Triple objects
with `unknown` instead of the configured target triple (e.g.,
`powerpc-ibm-aix7.3.0.0`). This results in Clang driver errors like
`error: unknown target triple 'unknown'`.

Used `Twine` constructor with braced initialization to bypass ambiguity.

---------

Co-authored-by: Tony Varghese <tony.varghese@ibm.com>
Co-authored-by: Matt Arsenault <arsenm2@gmail.com>

Author: 3 people

clang/test/Driver/aix-default-target-triple.c

@@ -0,0 +1,14 @@
+// Test for the Triple constructor ambiguity fix on AIX
+// This test verifies that the default target triple is correctly resolved
+// and doesn't fall back to "unknown" due to constructor ambiguity.
+
+// REQUIRES: system-aix
+// RUN: %clang -v %s -c 2>&1 | FileCheck %s --check-prefix=CHECK-TARGET
+
+// Test that the target triple contains AIX and is not "unknown"
+// The target should be something like "powerpc-ibm-aix7.3.0.0"
+// CHECK-TARGET: Target: {{.*}}aix{{.*}}
+
+int main() {
+    return 0;
+}

llvm/lib/TargetParser/Unix/Host.inc

@@ -55,7 +55,7 @@ static std::string updateTripleOSVersion(std::string TargetTripleString) {
   // On AIX, the AIX version and release should be that of the current host
   // unless if the version has already been specified.
   if (Triple(LLVM_HOST_TRIPLE).getOS() == Triple::AIX) {
-    Triple TT(std::move(TargetTripleString));
+    Triple TT{TargetTripleString};
     if (TT.getOS() == Triple::AIX && !TT.getOSMajorVersion()) {
       struct utsname name;
       if (uname(&name) != -1) {