Eliminate some flakes

- Get ASAN working on Windows.

- Deleting directories and then recreating them with the same name in a
  short period of time appears to be a no-no on Windows.

- There's no reason to call FlushFileBuffers on close() for pipes, and
  it's harmful since it might block indefinitely for no good reason.

libc/runtime/getdosenviron.c

@@ -18,6 +18,30 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/runtime/runtime.h"
 #include "libc/str/str.h"
+#include "libc/str/tpenc.h"
+#include "libc/str/utf16.h"
+
+static textwindows noasan axdx_t Recode16to8(char *dst, size_t dstsize,
+                                             const char16_t *src) {
+  axdx_t r;
+  uint64_t w;
+  wint_t x, y;
+  for (r.ax = 0, r.dx = 0;;) {
+    if (!(x = src[r.dx++])) break;
+    if (IsUtf16Cont(x)) continue;
+    if (!IsUcs2(x)) {
+      if (!(y = src[r.dx++])) break;
+      x = MergeUtf16(x, y);
+    }
+    for (w = tpenc(x); w && r.ax + 1 < dstsize; w >>= 8) {
+      dst[r.ax++] = w & 0xFF;
+    }
+  }
+  if (r.ax < dstsize) {
+    dst[r.ax] = 0;
+  }
+  return r;
+}
 
 /**
  * Transcodes NT environment variable block from UTF-16 to UTF-8.
@@ -29,8 +53,8 @@
  * @param max is the pointer count capacity of envp
  * @return number of variables decoded, excluding NULL-terminator
  */
-textwindows int GetDosEnviron(const char16_t *env, char *buf, size_t size,
-                              char **envp, size_t max) {
+textwindows noasan int GetDosEnviron(const char16_t *env, char *buf,
+                                     size_t size, char **envp, size_t max) {
   int i;
   axdx_t r;
   i = 0;
@@ -38,7 +62,7 @@ textwindows int GetDosEnviron(const char16_t *env, char *buf, size_t size,
     --size;
     while (*env) {
       if (i + 1 < max) envp[i++] = buf;
-      r = tprecode16to8(buf, size, env);
+      r = Recode16to8(buf, size, env);
       size -= r.ax + 1;
       buf += r.ax + 1;
       env += r.dx;