[sanitizer] Refactor GNU libc version retrieval

[Lekensteyn]

Summary

Use gnu_get_libc_version (since GNU libc 2.1) instead of confstr because
the latter is intercepted by msan and therefore less suitable for reuse.

No functional change intended.

[Lekensteyn]

Superseded by https://reviews.llvm.org/D48265

[vitalybuka]

In D48254#1134845, @Lekensteyn wrote:

Superseded by https://reviews.llvm.org/D48265

Sorry, I have not noticed your patches.

lib/sanitizer_common/sanitizer_linux_libcdep.cc

 #endif
 #endif
 
 #if !SANITIZER_ANDROID
 #include <elf.h>
 #include <unistd.h>
 #endif
 
+#ifdef __GLIBC__
+#include <gnu/libc-version.h>
+#endif
+
 namespace __sanitizer {
 
 SANITIZER_WEAK_ATTRIBUTE int
 real_sigaction(int signum, const void *act, void *oldact);
 
 int internal_sigaction(int signum, const void *act, void *oldact) {
 #if !SANITIZER_GO
   if (&real_sigaction)
bool SetEnv(const char *name, const char *value) {
   typedef int(*setenv_ft)(const char *name, const char *value, int overwrite);
   setenv_ft setenv_f;
   CHECK_EQ(sizeof(setenv_f), sizeof(f));
   internal_memcpy(&setenv_f, &f, sizeof(f));
   return setenv_f(name, value, 1) == 0;
 }
 #endif
 
+int GetGlibcVersion(int *patch) {
+  if (patch)
+    *patch = 0;
+#ifdef __GLIBC__
+  const char *version = gnu_get_libc_version();
+  if (version[0] == '2' && version[1] == '.') {
+    char *end;
+    int minor = internal_simple_strtoll(version + 2, &end, 10);
+    if (end != version + 2 && (*end == '\0' || *end == '.' || *end == '-')) {
+      if (*end == '.' && patch)
+        // strtoll will return 0 if no valid conversion could be performed
+        *patch = internal_simple_strtoll(end + 1, nullptr, 10);
+      return minor;
+    }
+  }
+#endif // __GLIBC__
+  return 0;
+}
+
 #if !SANITIZER_FREEBSD && !SANITIZER_ANDROID && !SANITIZER_GO &&               \
     !SANITIZER_NETBSD && !SANITIZER_OPENBSD && !SANITIZER_SOLARIS
 static uptr g_tls_size;
 
 #ifdef __i386__
 # ifndef __GLIBC_PREREQ
 #  define CHECK_GET_TLS_STATIC_INFO_VERSION 1
 # else

 // sizeof(struct pthread) from glibc.
 static atomic_uintptr_t thread_descriptor_size;
 
 uptr ThreadDescriptorSize() {
   uptr val = atomic_load_relaxed(&thread_descriptor_size);
   if (val)
     return val;
 #if defined(__x86_64__) || defined(__i386__) || defined(__arm__)
-#ifdef _CS_GNU_LIBC_VERSION
-  char buf[64];
-  uptr len = confstr(_CS_GNU_LIBC_VERSION, buf, sizeof(buf));
-  if (len < sizeof(buf) && internal_strncmp(buf, "glibc 2.", 8) == 0) {
-    char *end;
-    int minor = internal_simple_strtoll(buf + 8, &end, 10);
-    if (end != buf + 8 && (*end == '\0' || *end == '.' || *end == '-')) {
-      int patch = 0;
-      if (*end == '.')
-        // strtoll will return 0 if no valid conversion could be performed
-        patch = internal_simple_strtoll(end + 1, nullptr, 10);
-
-      /* sizeof(struct pthread) values from various glibc versions.  */
-      if (SANITIZER_X32)
-        val = 1728;  // Assume only one particular version for x32.
-      // For ARM sizeof(struct pthread) changed in Glibc 2.23.
-      else if (SANITIZER_ARM)
-        val = minor <= 22 ? 1120 : 1216;
-      else if (minor <= 3)
-        val = FIRST_32_SECOND_64(1104, 1696);
-      else if (minor == 4)
-        val = FIRST_32_SECOND_64(1120, 1728);
-      else if (minor == 5)
-        val = FIRST_32_SECOND_64(1136, 1728);
-      else if (minor <= 9)
-        val = FIRST_32_SECOND_64(1136, 1712);
-      else if (minor == 10)
-        val = FIRST_32_SECOND_64(1168, 1776);
-      else if (minor == 11 || (minor == 12 && patch == 1))
-        val = FIRST_32_SECOND_64(1168, 2288);
-      else if (minor <= 13)
-        val = FIRST_32_SECOND_64(1168, 2304);
-      else
-        val = FIRST_32_SECOND_64(1216, 2304);
-    }
-  }
+#ifdef __GLIBC__
+  int minor = GetGlibcVersion(&patch);
+  if (minor) {
 #endif
 #elif defined(__mips__)
   // TODO(sagarthakur): add more values as per different glibc versions.
   val = FIRST_32_SECOND_64(1152, 1776);
 #elif defined(__aarch64__)
   // The sizeof (struct pthread) is the same from GLIBC 2.17 to 2.22.
   val = 1776;
 #elif defined(__powerpc64__)