[llvm] [cmake] Add pthread to required libraries before dl and rt checks (PR #203054)

[Reid Kleckner via llvm-commits]

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@@ -160,8 +155,22 @@ if(HAVE_LIBPTHREAD)
   set(THREADS_HAVE_PTHREAD_ARG Off)
   find_package(Threads REQUIRED)
   set(LLVM_PTHREAD_LIB ${CMAKE_THREAD_LIBS_INIT})
+  if(LLVM_PTHREAD_LIB)
+    list(APPEND CMAKE_REQUIRED_LIBRARIES ${LLVM_PTHREAD_LIB})
+  endif()
+endif()
+
+# Keep the dlopen and rt library checks after FindThreads so that
+# CMAKE_REQUIRED_LIBRARIES includes pthread. glibc versions before 2.34 may
+# need pthread to satisfy librt dependencies.
+if(NOT WIN32)
+  check_library_exists(dl dlopen "" HAVE_LIBDL)
+  check_library_exists(rt shm_open "" HAVE_LIBRT)
 endif()
 
+# Check for libpfm.
+include(FindLibpfm)
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rnk wrote:

I think it makes sense, the idea here was to move all the pthread detection code into one block, instead of having a long block of unrelated library detection checks.

https://github.com/llvm/llvm-project/pull/203054