Always use compiler builtin for offsetof()

We have received multiple reports of GCC breaking builds when compiler
flags like `-std=c11` were being passed. The workaround until the next
release is to simply not define `__STRICT_ANSI__` which is a bad idea.

libc/integral/c.inc

@@ -473,12 +473,7 @@ typedef struct {
 #define autotype(x) typeof(x)
 #endif
 
-#if defined(__STRICT_ANSI__) || \
-    (!defined(__GNUC__) && !defined(__builtin_offsetof))
-#define offsetof(type, member) ((unsigned long)&((type *)0)->member)
-#else
 #define offsetof(type, member) __builtin_offsetof(type, member)
-#endif
 
 #ifdef _COSMO_SOURCE
 

libc/thread/pthread_cancel.c

@@ -71,7 +71,7 @@ static void _pthread_cancel_sig(int sig, siginfo_t *si, void *arg) {
   if (pt->pt_flags & PT_NOCANCEL) return;
   if (!atomic_load_explicit(&pt->pt_canceled, memory_order_acquire)) return;
 
-  // in asynchronous mode we'll just the exit asynchronously
+  // in asynchronous mode the asynchronous signal calls exit
   if (pt->pt_flags & PT_ASYNC) {
     sigaddset(&ctx->uc_sigmask, SIGTHR);
     pthread_sigmask(SIG_SETMASK, &ctx->uc_sigmask, 0);