[compiler-rt] Reapply "[NFC][sanitizer] Switch to `gnu_get_libc_version` (#108724)" (PR #108885)

[Vitaly Buka via llvm-commits]

https://github.com/vitalybuka created https://github.com/llvm/llvm-project/pull/108885

In #108724 `#ifdef` was used instead of `#if`.

This reverts commit 68e4518598d63efa02230f400e50263baccbb8e4.


>From 56e9e88b019839dcea9ae1ff5290d190a169fa0b Mon Sep 17 00:00:00 2001
From: Vitaly Buka <vitalybuka at google.com>
Date: Mon, 16 Sep 2024 14:12:51 -0700
Subject: [PATCH] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20initia?=
 =?UTF-8?q?l=20version?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Created using spr 1.3.4
---
 .../sanitizer_linux_libcdep.cpp                | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp
index 51c1f9ff111de9..21bd2a23f5763c 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp
@@ -40,6 +40,10 @@
 #  include <sys/resource.h>
 #  include <syslog.h>
 
+#  if SANITIZER_GLIBC
+#    include <gnu/libc-version.h>
+#  endif
+
 #  if !defined(ElfW)
 #    define ElfW(type) Elf_##type
 #  endif
@@ -198,17 +202,11 @@ bool SetEnv(const char *name, const char *value) {
 
 __attribute__((unused)) static bool GetLibcVersion(int *major, int *minor,
                                                    int *patch) {
-#  ifdef _CS_GNU_LIBC_VERSION
-  char buf[64];
-  uptr len = confstr(_CS_GNU_LIBC_VERSION, buf, sizeof(buf));
-  if (len >= sizeof(buf))
-    return false;
-  buf[len] = 0;
-  static const char kGLibC[] = "glibc ";
-  if (internal_strncmp(buf, kGLibC, sizeof(kGLibC) - 1) != 0)
-    return false;
-  const char *p = buf + sizeof(kGLibC) - 1;
+#  if SANITIZER_GLIBC
+  const char *p = gnu_get_libc_version();
   *major = internal_simple_strtoll(p, &p, 10);
+  // Caller does not expect anything else.
+  CHECK_EQ(*major, 2);
   *minor = (*p == '.') ? internal_simple_strtoll(p + 1, &p, 10) : 0;
   *patch = (*p == '.') ? internal_simple_strtoll(p + 1, &p, 10) : 0;
   return true;