Update comment about __sync_lock_test_and_set() bug.
State the earliest known fixed version, so we can someday judge the
workaround to be obsolete.
/*
* gcc or compatible, including clang and icc. Exclude xlc. The ppc64le "IBM
* XL C/C++ for Linux, V13.1.2" emulates gcc, but __sync_lock_test_and_set()
- * of one-byte types elicits SIGSEGV.
+ * of one-byte types elicits SIGSEGV. That bug was gone by V13.1.5 (2016-12).
*/
#if (defined(__GNUC__) || defined(__INTEL_COMPILER)) && !(defined(__IBMC__) || defined(__IBMCPP__))
#include "port/atomics/generic-gcc.h"
