libc: Add syscall wrappers for unlinkat() and openat()

libc/include/fcntl.h

@@ -16,6 +16,9 @@ extern "C"
     /* Open a file path and return a file descriptor to it. */
     int open(const char* path, int flags, ...);
 
+    /* Open a file path relative to a file descriptor and return a file descriptor to it. */
+    int openat(int dirfd, const char* path, int flags, ...);
+
     /* Create a file and return a file descriptor to it. */
     int creat(const char* path, mode_t mode);
 

libc/include/unistd.h

@@ -115,6 +115,9 @@ extern "C"
     /* Remove a name from the filesystem. */
     int unlink(const char* path);
 
+    /* Remove a name or directory from the filesystem. */
+    int unlinkat(int dirfd, const char* path, int flags);
+
     /* Remove a directory from the filesystem. */
     int rmdir(const char* path);
 

libc/src/fcntl.cpp

@@ -19,9 +19,22 @@ extern "C"
         __errno_return(rc, int);
     }
 
+    int openat(int dirfd, const char* path, int flags, ...)
+    {
+        va_list ap;
+        va_start(ap, flags);
+
+        mode_t mode = (mode_t)va_arg(ap, int);
+
+        long rc = syscall(SYS_openat, dirfd, path, flags, mode);
+
+        va_end(ap);
+        __errno_return(rc, int);
+    }
+
     int creat(const char* path, mode_t mode)
     {
-        return open(path, O_WRONLY | O_CREAT | O_TRUNC, mode);
+        return openat(AT_FDCWD, path, O_WRONLY | O_CREAT | O_TRUNC, mode);
     }
 
     int fcntl(int fd, int cmd, ...)

libc/src/unistd.cpp

@@ -370,14 +370,18 @@ extern "C"
 
     int unlink(const char* path)
     {
-        long rc = syscall(SYS_unlinkat, AT_FDCWD, path, 0);
+        return unlinkat(AT_FDCWD, path, 0);
+    }
+
+    int unlinkat(int dirfd, const char* path, int flags)
+    {
+        long rc = syscall(SYS_unlinkat, dirfd, path, flags);
         __errno_return(rc, int);
     }
 
     int rmdir(const char* path)
     {
-        long rc = syscall(SYS_unlinkat, AT_FDCWD, path, AT_REMOVEDIR);
-        __errno_return(rc, int);
+        return unlinkat(AT_FDCWD, path, AT_REMOVEDIR);
     }
 
     int gethostname(char* buf, size_t len)