Remove file_create and add file_mkdir.

Besides being a slight simplification (the only current use of
`file_create` is creating directories), if we add ways to create
other kinds of filesystem objects in the future, it's desirable
to create separate functions for them.

WASI has two levels of capabilities -- static and dynamic. The
static capabilities are the imports. By using separate functions
for separate file types, we can distinguish between the
capabilities to create different types of filesystem objects
statically.

And, users won't often need to specify what type of thing to create
dynamicaly. For example, the POSIX interface just has `mkdir`.

Author: sunfishcode

expected/wasm32-wasi/undefined-symbols.txt

@@ -39,8 +39,8 @@ __wasi_fd_sync
 __wasi_fd_write
 __wasi_file_advise
 __wasi_file_allocate
-__wasi_file_create
 __wasi_file_link
+__wasi_file_mkdir
 __wasi_file_open
 __wasi_file_readdir
 __wasi_file_readlink

libc-bottom-half/cloudlibc/src/libc/sys/stat/mkdirat.c

@@ -15,8 +15,13 @@ int mkdirat(int fd, const char *path, ...) {
 #else
 int mkdirat(int fd, const char *path, mode_t mode) {
 #endif
+#ifdef __wasilibc_unmodified_upstream // __wasi_file_mkdir
   __wasi_errno_t error = __wasi_file_create(
       fd, path, strlen(path), __WASI_FILETYPE_DIRECTORY);
+#else
+  __wasi_errno_t error = __wasi_file_mkdir(
+      fd, path, strlen(path));
+#endif
   if (error != 0) {
     errno = errno_fixup_directory(fd, error);
     return -1;

libc-bottom-half/headers/public/wasi.h

@@ -639,12 +639,11 @@ __wasi_errno_t __wasi_file_allocate(
     __wasi_filesize_t len
 ) __WASI_SYSCALL_NAME(file_allocate) __attribute__((__warn_unused_result__));
 
-__wasi_errno_t __wasi_file_create(
+__wasi_errno_t __wasi_file_mkdir(
     __wasi_fd_t fd,
     const char *path,
-    size_t path_len,
-    __wasi_filetype_t type
-) __WASI_SYSCALL_NAME(file_create) __attribute__((__warn_unused_result__));
+    size_t path_len
+) __WASI_SYSCALL_NAME(file_mkdir) __attribute__((__warn_unused_result__));
 
 __wasi_errno_t __wasi_file_link(
     __wasi_fd_t old_fd,