Fix comment in rtl.def

Commit r210360 removed the first "i" field from the various instruction
nodes in rtx.def, moving it to an explicit "int insn_uid;" field
of the union "u2" within rtx_def.

Update the comment in rtl.def to reflect this change.  Also, fix
a stray apostrophe.

gcc/ChangeLog:
	* rtl.def: Update comment for "things in the instruction chain" to
	reflect the removal of the leading "i" field for INSN_UID in
	r210360.  Fix bogus apostrophe.

From-SVN: r235520

gcc/ChangeLog

+2016-04-27  David Malcolm  <dmalcolm@redhat.com>
+
+	* rtl.def: Update comment for "things in the instruction chain" to
+	reflect the removal of the leading "i" field for INSN_UID in
+	r210360.  Fix bogus apostrophe.
+
 2016-04-27  Uros Bizjak  <ubizjak@gmail.com>
 
 	* config/i386/i386.md

gcc/rtl.def

@@ -131,10 +131,10 @@ DEF_RTL_EXPR(ADDRESS, "address", "i", RTX_EXTRA)
 /* ----------------------------------------------------------------------
    Expression types used for things in the instruction chain.
 
-   All formats must start with "iuu" to handle the chain.
+   All formats must start with "uu" to handle the chain.
    Each insn expression holds an rtl instruction and its semantics
    during back-end processing.
-   See macros's in "rtl.h" for the meaning of each rtx->u.fld[].
+   See macros in "rtl.h" for the meaning of each rtx->u.fld[].
 
    ---------------------------------------------------------------------- */