Disable the tests for fork detection on Linux < 4.14.

Apparently we have some on CQ.

Change-Id: I915310ad9ca73f04538fa6eadc5abb4e6a6a6964
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/94987
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
Auto-Submit: Rudolf Polzer <rpolzer@google.com>

crypto/rand/fork_detect_test.cc

diff --git a/crypto/rand/fork_detect_test.cc b/crypto/rand/fork_detect_test.cc
index 81bcb0d..15f3fc0 100644
--- a/crypto/rand/fork_detect_test.cc
+++ b/crypto/rand/fork_detect_test.cc
@@ -30,12 +30,18 @@
 #include <unistd.h>
 
 #include <functional>
+#include <tuple>
 
 #if defined(OPENSSL_THREADS)
 #include <thread>
 #include <vector>
 #endif
 
+#if defined(OPENSSL_LINUX)
+#include <stdlib.h>
+#include <sys/utsname.h>
+#endif
+
 #include <gtest/gtest.h>
 
 #include <openssl/mem.h>
@@ -146,6 +152,21 @@
 
 TEST(ForkDetect, OSSupport) {
   uint64_t start = CRYPTO_get_fork_generation();
+#if defined(OPENSSL_LINUX)
+  if (start == 0) {
+    struct utsname u;
+    if (uname(&u) == 0) {
+      const char *dot = strchr(u.release, '.');
+      if (dot != nullptr) {
+        auto version = std::tuple(atoi(u.release), atoi(dot + 1));
+        if (version < std::tuple(4, 14)) {
+          GTEST_SKIP() << "Fork detection not supported on Linux " << u.release
+                       << " which is < 4.14. Skipping test.\n";
+        }
+      }
+    }
+  }
+#endif
   EXPECT_NE(start, uint64_t{0})
       << "Fork detection not supported, but support is configured to be "
          "expected on this platform in crypto/rand/internal.h. Typically this "