[llvm] Add check for SYS_gettid support (PR #119742)

[Brad Smith via llvm-commits]

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@@ -140,7 +140,7 @@ uint64_t llvm::get_threadid() {
   return uint64_t(getthrid());
 #elif defined(__ANDROID__)
   return uint64_t(gettid());
-#elif defined(__linux__)
+#elif defined(__linux__) && defined(SYS_gettid)
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brad0 wrote:

It would be better to change SYS_gettid to __NR_gettid.

https://github.com/llvm/llvm-project/pull/119742