Kernel/LibC: Implement pwrite and make pread non-locking

userspace/libraries/LibC/include/sys/syscall.h

@@ -60,6 +60,7 @@ __BEGIN_DECLS
 	O(SYS_READLINKAT,		readlinkat)		\
 	O(SYS_MSYNC,			msync)			\
 	O(SYS_PREAD,			pread)			\
+	O(SYS_PWRITE,			pwrite)			\
 	O(SYS_FCHOWNAT,			fchownat)		\
 	O(SYS_LOAD_KEYMAP,		load_keymap)	\
 	O(SYS_SOCKET,			socket)			\

userspace/libraries/LibC/unistd.cpp

@@ -127,6 +127,11 @@ ssize_t pread(int fildes, void* buf, size_t nbyte, off_t offset)
 	return syscall(SYS_PREAD, fildes, buf, nbyte, offset);
 }
 
+ssize_t pwrite(int fildes, const void* buf, size_t nbyte, off_t offset)
+{
+	return syscall(SYS_PWRITE, fildes, buf, nbyte, offset);
+}
+
 off_t lseek(int fildes, off_t offset, int whence)
 {
 	return syscall(SYS_SEEK, fildes, offset, whence);