Revert "[NFC][sanitizer] Switch to gnu_get_libc_version (llvm#108724)"

This reverts commit 69f3244.

Reason: buildbot breakage because Android doesn't have <gnu/libc-version.h>
https://lab.llvm.org/buildbot/#/builders/186/builds/2381

(It's probably easy to fix but I don't readily have an Android device to test.)

Author: thurstond

compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp

@@ -40,10 +40,6 @@
 #  include <sys/resource.h>
 #  include <syslog.h>
 
-#  ifdef SANITIZER_GLIBC
-#    include <gnu/libc-version.h>
-#  endif
-
 #  if !defined(ElfW)
 #    define ElfW(type) Elf_##type
 #  endif
@@ -202,11 +198,17 @@ bool SetEnv(const char *name, const char *value) {
 
 __attribute__((unused)) static bool GetLibcVersion(int *major, int *minor,
                                                    int *patch) {
-#  ifdef SANITIZER_GLIBC
-  const char *p = gnu_get_libc_version();
+#  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;
   *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;