timespec_get tests: Add comment

[Bruno Haible]

On a Linux/x86_64 system, I once saw this unit test fail:

FAIL: test-timespec_get

../../gltests/test-timespec_get.c:49: assertion 'ts1.tv_sec <= tt2' failed
FAIL test-timespec_get (exit status: 134)

The failure probability is small (ca. 0.1% to 0.3%). I registered a glibc bug
about it.


2023-03-05  Bruno Haible  <bruno@clisp.org>

        timespec_get tests: Add comment.
        * tests/test-timespec_get.c: Add a comment regarding a glibc bug.

diff --git a/tests/test-timespec_get.c b/tests/test-timespec_get.c
index 1b20fe23c0..69b98c5c64 100644
--- a/tests/test-timespec_get.c
+++ b/tests/test-timespec_get.c
@@ -46,6 +46,8 @@ main (void)
   ASSERT (tt2 <= tt4);
 
   /* Verify that the tv_sec field of the result is the same as time(NULL).  */
+  /* Note: This assertion sometimes fails on glibc systems, see
+     https://sourceware.org/bugzilla/show_bug.cgi?id=30200  */
   ASSERT (ts1.tv_sec <= tt2);
   ASSERT (tt2 <= ts3.tv_sec);
   ASSERT (ts3.tv_sec <= tt4);