[libc] use PR_GET_AUXV only if UAPI provides it

[SchrodingerZhu]

No description provided.

[SchrodingerZhu]

Merge without review as a simple build fix

[llvmbot]

@llvm/pr-subscribers-libc

Author: Schrodinger ZHU Yifan (SchrodingerZhu)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/162492.diff

1 Files Affected:

• (modified) libc/src/__support/OSUtil/linux/auxv.h (+4-2)

diff --git a/libc/src/__support/OSUtil/linux/auxv.h b/libc/src/__support/OSUtil/linux/auxv.h
index 17108e2e54794..7fb996f01dd84 100644
--- a/libc/src/__support/OSUtil/linux/auxv.h
+++ b/libc/src/__support/OSUtil/linux/auxv.h
@@ -96,8 +96,9 @@ LIBC_INLINE void Vector::fallback_initialize_unsync() {
   }
   size_t avaiable_size = AUXV_MMAP_SIZE - sizeof(Entry);
 
-  // Attempt 1: use PRCTL to get the auxv.
-  // We guarantee that the vector is always padded with AT_NULL entries.
+// Attempt 1: use PRCTL to get the auxv.
+// We guarantee that the vector is always padded with AT_NULL entries.
+#ifdef PR_GET_AUXV
   long prctl_ret = syscall_impl<long>(SYS_prctl, PR_GET_AUXV,
                                       reinterpret_cast<unsigned long>(vector),
                                       avaiable_size, 0, 0);
@@ -105,6 +106,7 @@ LIBC_INLINE void Vector::fallback_initialize_unsync() {
     entries = vector;
     return;
   }
+#endif
 
   // Attempt 2: read /proc/self/auxv.
 #ifdef SYS_openat