Make improvements

- Introduce portable sched_getcpu() api
- Support GCC's __target_clones__ feature
- Make fma() go faster on x86 in default mode
- Remove some asan checks from core libraries
- WinMain() now ensures $HOME and $USER are defined

libc/stdio/rngset.c

@@ -45,9 +45,6 @@ dontasan void *rngset(void *b, size_t n, uint64_t seed(void), size_t reseed) {
   size_t m;
   uint64_t x, t = 0;
   unsigned char *p = b;
-  if (IsAsan()) {
-    __asan_verify(b, n);
-  }
   if (!seed) {
     t = reseed;
     reseed = -1;