[Driver][OpenMP] Fix OpenMP target-toolchain-option parser (llvm#115375)

## Description

This PR fixes a segmentation fault that occurs when passing options
requiring arguments via `-Xopenmp-target=<triple>`. The issue was that
the function `Driver::getOffloadArchs` did not properly parse the
extracted option, but instead assumed it was valid, leading to a crash
when incomplete arguments were provided.

## Backtrace

```sh
llvm-project/build/bin/clang++ main.cpp -fopenmp=libomp -fopenmp-targets=powerpc64le-ibm-linux-gnu -Xopenmp-target=powerpc64le-ibm-linux-gnu -o 
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.      Program arguments: llvm-project/build/bin/clang++ main.cpp -fopenmp=libomp -fopenmp-targets=powerpc64le-ibm-linux-gnu -Xopenmp-target=powerpc64le-ibm-linux-gnu -o
1.      Compilation construction
2.      Building compilation actions
 #0 0x0000562fb21c363b llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (llvm-project/build/bin/clang+++0x392f63b)
 #1 0x0000562fb21c0e3c SignalHandler(int) Signals.cpp:0:0
 rust-lang#2 0x00007fcbf6c81420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 rust-lang#3 0x0000562fb1fa5d70 llvm::opt::Option::matches(llvm::opt::OptSpecifier) const (llvm-project/build/bin/clang+++0x3711d70)
 rust-lang#4 0x0000562fb2a78e7d clang::driver::Driver::getOffloadArchs(clang::driver::Compilation&, llvm::opt::DerivedArgList const&, clang::driver::Action::OffloadKind, clang::driver::ToolChain const*, bool) const (llvm-project/build/bin/clang+++0x41e4e7d)
 rust-lang#5 0x0000562fb2a7a9aa clang::driver::Driver::BuildOffloadingActions(clang::driver::Compilation&, llvm::opt::DerivedArgList&, std::pair<clang::driver::types::ID, llvm::opt::Arg const*> const&, clang::driver::Action*) const (.part.1164) Driver.cpp:0:0
 rust-lang#6 0x0000562fb2a7c093 clang::driver::Driver::BuildActions(clang::driver::Compilation&, llvm::opt::DerivedArgList&, llvm::SmallVector<std::pair<clang::driver::types::ID, llvm::opt::Arg const*>, 16u> const&, llvm::SmallVector<clang::driver::Action*, 3u>&) const (llvm-project/build/bin/clang+++0x41e8093)
 rust-lang#7 0x0000562fb2a8395d clang::driver::Driver::BuildCompilation(llvm::ArrayRef<char const*>) (llvm-project/build/bin/clang+++0x41ef95d)
 rust-lang#8 0x0000562faf92684c clang_main(int, char**, llvm::ToolContext const&) (llvm-project/build/bin/clang+++0x109284c)
 rust-lang#9 0x0000562faf826cc6 main (llvm-project/build/bin/clang+++0xf92cc6)
rust-lang#10 0x00007fcbf6699083 __libc_start_main /build/glibc-LcI20x/glibc-2.31/csu/../csu/libc-start.c:342:3
rust-lang#11 0x0000562faf923a5e _start (llvm-project/build/bin/clang+++0x108fa5e)
[1]    2628042 segmentation fault (core dumped)   main.cpp -fopenmp=libomp -fopenmp-targets=powerpc64le-ibm-linux-gnu  -o
```

clang/lib/Driver/Driver.cpp

@@ -4515,7 +4515,13 @@ Driver::getOffloadArchs(Compilation &C, const llvm::opt::DerivedArgList &Args,
         ToolChain::getOpenMPTriple(Arg->getValue(0)) == TC->getTriple()) {
       Arg->claim();
       unsigned Index = Args.getBaseArgs().MakeIndex(Arg->getValue(1));
+      unsigned Prev = Index;
       ExtractedArg = getOpts().ParseOneArg(Args, Index);
+      if (!ExtractedArg || Index > Prev + 1) {
+        TC->getDriver().Diag(diag::err_drv_invalid_Xopenmp_target_with_args)
+            << Arg->getAsString(Args);
+        continue;
+      }
       Arg = ExtractedArg.get();
     }
 

clang/lib/Driver/ToolChain.cpp

@@ -1596,8 +1596,10 @@ llvm::opt::DerivedArgList *ToolChain::TranslateOpenMPTargetArgs(
     Prev = Index;
     std::unique_ptr<Arg> XOpenMPTargetArg(Opts.ParseOneArg(Args, Index));
     if (!XOpenMPTargetArg || Index > Prev + 1) {
-      getDriver().Diag(diag::err_drv_invalid_Xopenmp_target_with_args)
-          << A->getAsString(Args);
+      if (!A->isClaimed()) {
+        getDriver().Diag(diag::err_drv_invalid_Xopenmp_target_with_args)
+            << A->getAsString(Args);
+      }
       continue;
     }
     if (XOpenMPTargetNoTriple && XOpenMPTargetArg &&

clang/test/Driver/openmp-offload.c

@@ -84,9 +84,15 @@
 
 /// Check -Xopenmp-target triggers error when an option requiring arguments is passed to it.
 // RUN:   not %clang -### -no-canonical-prefixes -fopenmp=libomp -fopenmp-targets=powerpc64le-ibm-linux-gnu -Xopenmp-target -Xopenmp-target -mcpu=pwr8 %s 2>&1 \
-// RUN:   | FileCheck -check-prefix=CHK-FOPENMP-TARGET-NESTED-ERROR %s
+// RUN:   | FileCheck -check-prefix=CHK-FOPENMP-TARGET-NESTED-ERROR_0 %s
 
-// CHK-FOPENMP-TARGET-NESTED-ERROR: clang{{.*}} error: invalid -Xopenmp-target argument: '-Xopenmp-target -Xopenmp-target', options requiring arguments are unsupported
+// CHK-FOPENMP-TARGET-NESTED-ERROR_0: error: invalid -Xopenmp-target argument: '-Xopenmp-target -Xopenmp-target', options requiring arguments are unsupported
+
+/// Check -Xopenmp-target= triggers error when an option requiring arguments is passed to it.
+// RUN:   not %clang -### -no-canonical-prefixes -fopenmp=libomp -fopenmp-targets=powerpc64le-ibm-linux-gnu -Xopenmp-target=powerpc64le-ibm-linux-gnu -Xopenmp-target -mcpu=pwr8 %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHK-FOPENMP-TARGET-NESTED-ERROR_1 %s
+
+// CHK-FOPENMP-TARGET-NESTED-ERROR_1: error: invalid -Xopenmp-target argument: '-Xopenmp-target=powerpc64le-ibm-linux-gnu -Xopenmp-target', options requiring arguments are unsupported
 
 /// ###########################################################################