[clang] [compiler-rt] [llvm] [CMake] Use Clang to infer the target triple (PR #89425)

[YunQiang Su via cfe-commits]

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@@ -183,6 +183,24 @@ message(STATUS "LLVM default target triple: ${LLVM_DEFAULT_TARGET_TRIPLE}")
 
 set(LLVM_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}")
 
+if(CMAKE_C_COMPILER_ID MATCHES "Clang")
+  set(option_prefix "")
+  if (CMAKE_C_SIMULATE_ID MATCHES "MSVC")
+    set(option_prefix "/clang:")
+  endif()
+  set(print_target_triple ${CMAKE_C_COMPILER} ${option_prefix}--target=${LLVM_DEFAULT_TARGET_TRIPLE} ${option_prefix}-print-target-triple)
+  execute_process(COMMAND ${print_target_triple}
+    RESULT_VARIABLE result
+    OUTPUT_VARIABLE output
+    OUTPUT_STRIP_TRAILING_WHITESPACE)
+  if(result EQUAL 0)
+    set(LLVM_DEFAULT_TARGET_TRIPLE ${output})
+  else()
+    string(REPLACE ";" " " print_target_triple "${print_target_triple}")
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wzssyqa wrote:

Ditto.  I guess that we need to test on more target. As some target doesn't use the new filesystem struct.

https://github.com/llvm/llvm-project/pull/89425