fix a few linux compilation warnings

core/src/fxge/dib/fx_dib_composite.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
  
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "../../../include/fxge/fx_ge.h"
 #include "../../../include/fxcodec/fx_codec.h"
 #include "dib_int.h"
 const FX_BYTE g_GammaRamp[256] = {
@@ skipping 4131 matching lines @@
         clip_box = pClipRgn->GetBox();
     }
     CFX_ScanlineCompositor compositor;
     if (!compositor.Init(GetFormat(), pSrcBitmap->GetFormat(), width, pSrcBitmap->GetPalette(), 0, blend_type,
                          pClipMask != NULL, bRgbByteOrder, 0, pIccTransform)) {
         return FALSE;
     }
     int dest_Bpp = m_bpp / 8;
     int src_Bpp = pSrcBitmap->GetBPP() / 8;
     FX_BOOL bRgb = FALSE;
+    // TODO(tsepez): Unused bCymk warning here is troubling. Is CMYK supported properly?
     FX_BOOL bCmyk = FALSE;

[jun_fang, 2015/01/17 00:39:17]

One of bRgb and bCmyk is duplicated. Suggest to remove bRgb but keep bCmyk. It
needs to be updated at line 4171 too.

     if (src_Bpp > 1) {
         if (pSrcBitmap->IsCmykImage()) {
             bCmyk = TRUE;
         } else {
             bRgb = TRUE;
         }
     }
     CFX_DIBitmap* pSrcAlphaMask = pSrcBitmap->m_pAlphaMask;
     for (int row = 0; row < height; row ++) {
         FX_LPBYTE dest_scan = m_pBuffer + (dest_top + row) * m_Pitch + dest_left * dest_Bpp;
@@ skipping 429 matching lines @@
     }
     src_alpha_scan = m_pScanlineAlphaV;
     dest_alpha_scan = dest_alpha_buf;
     if (dest_alpha_scan) {
         for (i = 0; i < m_DestHeight; i ++) {
             *dest_alpha_scan = *src_alpha_scan++;
             dest_alpha_scan += y_alpha_step;
         }
     }
 }