tests: include fcntl.h for open(), O_RDWR, O_CLOEXEC and O_CREAT

musl libc (unlike glibc) requires explicitly incuding fcntl.h to define open(),
O_RDWR, O_CLOEXEC and O_CREAT. Otherwise the build fails with the errors:

| ../weston-9.0.0/tests/weston-test-fixture-compositor.c: In function 'wait_for_lock':
| ../weston-9.0.0/tests/weston-test-fixture-compositor.c:135:7: warning: implicit declaration of function 'open'; did you mean 'popen'? [-Wimplicit-function-declaration]
|   135 |  fd = open(lock_path, O_RDWR | O_CLOEXEC | O_CREAT, 00700);
|       |       ^~~~
|       |       popen
| ../weston-9.0.0/tests/weston-test-fixture-compositor.c:135:23: error: 'O_RDWR' undeclared (first use in this function)
|   135 |  fd = open(lock_path, O_RDWR | O_CLOEXEC | O_CREAT, 00700);
|       |                       ^~~~~~
| ../weston-9.0.0/tests/weston-test-fixture-compositor.c:135:23: note: each undeclared identifier is reported only once for each function it appears in
| ../weston-9.0.0/tests/weston-test-fixture-compositor.c:135:32: error: 'O_CLOEXEC' undeclared (first use in this function)
|   135 |  fd = open(lock_path, O_RDWR | O_CLOEXEC | O_CREAT, 00700);
|       |                                ^~~~~~~~~
| ../weston-9.0.0/tests/weston-test-fixture-compositor.c:135:44: error: 'O_CREAT' undeclared (first use in this function)
|   135 |  fd = open(lock_path, O_RDWR | O_CLOEXEC | O_CREAT, 00700);
|       |                                            ^~~~~~~

Signed-off-by: Denys Dmytriyenko <denys@ti.com>

tests/weston-test-fixture-compositor.c

@@ -35,6 +35,7 @@
 #include <stdarg.h>
 #include <stdlib.h>
 #include <errno.h>
+#include <fcntl.h>
 
 #include "shared/helpers.h"
 #include "weston-test-fixture-compositor.h"