LibC: Add _PC* definitions to unistd.h

These are not used for anything yet

userspace/libraries/LibC/include/unistd.h

@@ -106,7 +106,30 @@ __BEGIN_DECLS
 
 // FIXME: _CS prefixed definitions
 
-// FIXME: _PC prefixed definitions
+enum
+{
+	_PC_2_SYMLINKS,
+	_PC_ALLOC_SIZE_MIN,
+	_PC_ASYNC_IO,
+	_PC_CHOWN_RESTRICTED,
+	_PC_FILESIZEBITS,
+	_PC_LINK_MAX,
+	_PC_MAX_CANON,
+	_PC_MAX_INPUT,
+	_PC_NAME_MAX,
+	_PC_NO_TRUNC,
+	_PC_PATH_MAX,
+	_PC_PIPE_BUF,
+	_PC_PRIO_IO,
+	_PC_REC_INCR_XFER_SIZE,
+	_PC_REC_MAX_XFER_SIZE,
+	_PC_REC_MIN_XFER_SIZE,
+	_PC_REC_XFER_ALIGN,
+	_PC_SYMLINK_MAX,
+	_PC_SYNC_IO,
+	_PC_TIMESTAMP_RESOLUTION,
+	_PC_VDISABLE,
+};
 
 #define F_OK 0x01
 #define R_OK 0x02