sdk/rust: Fix hostfs create_file() failing with EEXIST on existing files

Replace O_EXCL with O_TRUNC in create_file for both Linux and Darwin
hostfs backends. The FUSE create op is called by the kernel for
open(O_CREAT) on existing files (e.g. cargo overwriting .d dependency
files), so create_file needs to truncate rather than fail. Higher-level
callers already guard against unwanted overwrites with their own
existence checks.

Author: penberg

sdk/rust/src/filesystem/hostfs_darwin.rs

@@ -673,7 +673,7 @@ impl FileSystem for HostFS {
         let file_fd = unsafe {
             libc::open(
                 c_path.as_ptr(),
-                libc::O_CREAT | libc::O_EXCL | libc::O_RDWR,
+                libc::O_CREAT | libc::O_TRUNC | libc::O_RDWR,
                 mode as libc::mode_t as libc::c_uint,
             )
         };

sdk/rust/src/filesystem/hostfs_linux.rs

@@ -711,7 +711,7 @@ impl FileSystem for HostFS {
             libc::openat(
                 parent_fd,
                 c_name.as_ptr(),
-                libc::O_CREAT | libc::O_EXCL | libc::O_RDWR,
+                libc::O_CREAT | libc::O_TRUNC | libc::O_RDWR,
                 mode as libc::mode_t,
             )
         };