Reduce warnings relevant to Zephyr platform

[kr-t]

This PR is intended to remove following warnings, when build in Zephyr application:

wasm-micro-runtime/core/shared/platform/zephyr/platform_internal.h:293: warning: "CLOCK_MONOTONIC" redefined
  293 | #define CLOCK_MONOTONIC 4
wasm-micro-runtime/core/shared/platform/zephyr/zephyr_file.c: In function 'zephyr_fs_alloc_obj':
wasm-micro-runtime/core/shared/platform/zephyr/zephyr_file.c:123:25: warning: implicit declaration of function 'bh_strdup' [-Wimplicit-function-declaration]
  123 |             ptr->path = bh_strdup(path);
      |                         ^~~~~~~~~
wasm-micro-runtime/core/shared/platform/zephyr/zephyr_file.c:123:23: warning: assignment to 'char *' from 'int' makes pointer from integer without a cast [-Wint-conversion]
  123 |             ptr->path = bh_strdup(path);
      |                       ^
wasm-micro-runtime/core/shared/platform/zephyr/zephyr_file.c: In function 'os_renameat':
wasm-micro-runtime/core/shared/platform/zephyr/zephyr_file.c:853:35: warning: initialization of 'char *' from 'int' makes pointer from integer without a cast [-Wint-conversion]
  853 |             char *new_path_copy = bh_strdup(new_path);
      |                                   ^~~~~~~~~
[45/462] Building C object CMakeFiles/app.dir/wasm-micro-runtime/core/iwasm/libraries/libc-wasi/sandboxed-system-primitives/src/posix.c.obj
wasm-micro-runtime/core/iwasm/libraries/libc-wasi/sandboxed-system-primitives/src/posix.c: In function 'wasmtime_ssp_poll_oneoff':
wasm-micro-runtime/core/iwasm/libraries/libc-wasi/sandboxed-system-primitives/src/posix.c:2216:42: warning: initialization of 'os_file_handle' {aka 'struct zephyr_handle *'} from 'int' makes pointer from integer without a cast [-Wint-conversion]
 2216 |                     os_file_handle tfd = fos[i]->file_handle->fd;
      |                                          ^~~
wasm-micro-runtime/core/iwasm/libraries/libc-wasi/sandboxed-system-primitives/src/posix.c:2222:31: warning: initialization of 'int' from 'os_file_handle' {aka 'struct zephyr_handle *'} makes integer from pointer without a cast [-Wint-conversion]
 2222 |                         .fd = tfd,
      |                               ^~~
wasm-micro-runtime/core/iwasm/libraries/libc-wasi/sandboxed-system-primitives/src/posix.c:2222:31: note: (near initialization for '(anonymous).fd')

Result - no warnings.

Tested in ocre as a zephyr application.

Updates:
there have been updates and changes after the initial commit and initial description. Please check those below in my follow-up comments.

[kr-t]

Update after the initial commit:

Apparently, the CI doesn't like that in Zephyr's case I used int instead of os_file_handle. I have tried another way of refactoring the logic of how we abstract the os_file_handle tfd variable, but each time I have successfully removed warnings, the CI was unhappy with my changes and I couldn't pass all checks. Therefore, the changes in this PR in its current state leaves us with following - a successful CI, reduced amount of warnings and following warnings left:

wasm-micro-runtime/core/iwasm/libraries/libc-wasi/sandboxed-system-primitives/src/posix.c:2216:42: warning: initialization of 'os_file_handle' {aka 'struct zephyr_handle *'} from 'int' makes pointer from integer without a cast [-Wint-conversion]
 2216 |                     os_file_handle tfd = fos[i]->file_handle->fd;
      |                                          ^~~
wasm-micro-runtime/core/iwasm/libraries/libc-wasi/sandboxed-system-primitives/src/posix.c:2222:31: warning: initialization of 'int' from 'os_file_handle' {aka 'struct zephyr_handle *'} makes integer from pointer without a cast [-Wint-conversion]
 2222 |                         .fd = tfd,
      |                               ^~~
wasm-micro-runtime/core/iwasm/libraries/libc-wasi/sandboxed-system-primitives/src/posix.c:2222:31: note: (near initialization for '(anonymous).fd')

Fixing temporary workaround which was made in PR#4377 will probably help with these remaining warnings as well.

[lum1n0us]

IMM, a better approach is to avoid using bh_xxx() functions in zephyr/zephyr_file.c. Instead, opt for a specific version that is compatible with Zephyr

[kr-t]

Noted, will check out the alternatives.

[kr-t]

Removed bh_strdup() function, therefore reducing the undeclared warning.
Since zephyr supports strdup() only when CONFIG_POSIX_C_LIB_EXT is selected, I didn't want to force users to use this, so I replaced strdup() with more generic strcpy().