FIx riscv port building with the trunk

[Jeff Law <law at redhat dot com>]

RISCV targets were failing to build due to implicit-fallthru warnings.

This changes comments which indicated expected fallthru to use the 
attribute and the port builds again.   I assume something about the use 
of the cpp macro is causing the comment to not have the intended effect. 
 I didn't dig into that.  Nor did I try to change all the fallthru 
comments to use the attribute -- just the two that implicit-fallthru was 
complaining about.

Verified that after this patch the two riscv targets build.  Installed 
on the trunk.

Jeff

commit 448373f1f2912228dc72605fb6f3343fd57023ee
Author: law <law@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Mon Mar 13 17:49:40 2017 +0000

            * config/riscv/riscv.c (riscv_emit_float_compare): Use fallthru
            attribute rather than comments.
    
    git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@246101 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 124dca3..e863cdf 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,8 @@
 2017-03-13  Jeff Law  <law@redhat.com>
 
+	* config/riscv/riscv.c (riscv_emit_float_compare): Use fallthru
+	attribute rather than comments.
+
 	* config/pdp11/pdp11.md (movmemhi): Adjust operand numbers to
 	match_scratch operand is highest.
 
diff --git a/gcc/config/riscv/riscv.c b/gcc/config/riscv/riscv.c
index 89567f7..e5044ba 100644
--- a/gcc/config/riscv/riscv.c
+++ b/gcc/config/riscv/riscv.c
@@ -2089,13 +2089,13 @@ riscv_emit_float_compare (enum rtx_code *code, rtx *op0, rtx *op1)
 
     case UNLT:
       std::swap (cmp_op0, cmp_op1);
-      /* Fall through.  */
+      __attribute__((fallthrough));
 
     UNORDERED_COMPARISON(UNGT, le)
 
     case UNLE:
       std::swap (cmp_op0, cmp_op1);
-      /* Fall through.  */
+      __attribute__((fallthrough));
 
     UNORDERED_COMPARISON(UNGE, lt)
 #undef UNORDERED_COMPARISON