Fix popen_test in MODE=dbg

ASAN and vfork() don't appear to play well together. Maybe in later
versions of GCC it'll be better. But vfork() is flirting with danger
after all and that probably doesn't make sense in ASAN mode anyway.

libc/stdio/fgetc.c

@@ -23,11 +23,11 @@
  * @return byte in range 0..255, or -1 w/ errno
  */
 int fgetc(FILE *f) {
-  unsigned char b;
+  unsigned char b[1];
   if (f->beg < f->end) {
     return f->buf[f->beg++] & 0xff;
   } else {
-    if (!fread(&b, 1, 1, f)) return -1;
-    return b;
+    if (!fread(b, 1, 1, f)) return -1;
+    return b[0];
   }
 }

libc/stdio/popen.c

@@ -33,7 +33,7 @@
  */
 FILE *popen(const char *cmdline, const char *mode) {
   FILE *f;
-  int dir, flags, pipefds[2];
+  int e, pid, dir, flags, pipefds[2];
   flags = fopenflags(mode);
   if ((flags & O_ACCMODE) == O_RDONLY) {
     dir = 0;
@@ -45,13 +45,28 @@ FILE *popen(const char *cmdline, const char *mode) {
   }
   if (pipe(pipefds) == -1) return NULL;
   fcntl(pipefds[dir], F_SETFD, FD_CLOEXEC);
-  if (!(f = fdopen(pipefds[dir], mode))) abort();
-  if ((f->pid = vfork()) == -1) abort();
-  if (!f->pid) {
-    dup2(pipefds[!dir], !dir);
-    systemexec(cmdline);
-    _exit(127);
+  if ((f = fdopen(pipefds[dir], mode))) {
+    switch ((pid = vfork())) {
+      case 0:
+        dup2(pipefds[!dir], !dir);
+        systemexec(cmdline);
+        _exit(127);
+      default:
+        f->pid = pid;
+        close(pipefds[!dir]);
+        return f;
+      case -1:
+        e = errno;
+        fclose(f);
+        close(pipefds[!dir]);
+        errno = e;
+        return NULL;
+    }
+  } else {
+    e = errno;
+    close(pipefds[0]);
+    close(pipefds[1]);
+    errno = e;
+    return NULL;
   }
-  close(pipefds[!dir]);
-  return f;
 }

libc/stdio/stdio.h

@@ -14,7 +14,7 @@ COSMOPOLITAN_C_START_
 
 typedef struct FILE {
   uint8_t bufmode; /* 0x00 _IOFBF, etc. (ignored if fd=-1) */
-  bool noclose;    /* 0x01 for fake dup() */
+  bool noclose;    /* 0x01 for fake dup() todo delete! */
   uint32_t iomode; /* 0x04 O_RDONLY, etc. (ignored if fd=-1) */
   int32_t state;   /* 0x08 0=OK, -1=EOF, >0=errno */
   int fd;          /* 0x0c ≥0=fd, -1=closed|buffer */