skip neon code in libwebp when neon is explicitly unavailable

This patch makes it possible to build libwebp without runtime neon detection/usage.

Review URL: https://codereview.chromium.org/95873002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242079 0039d316-1c4b-4281-b951-d872f2087c98

third_party/libwebp/dsp/dec.c

@@ -697,7 +697,9 @@ VP8SimpleFilterFunc VP8SimpleVFilter16i;
 VP8SimpleFilterFunc VP8SimpleHFilter16i;
 
 extern void VP8DspInitSSE2(void);
+#if defined(WEBP_USE_NEON)
 extern void VP8DspInitNEON(void);
+#endif
 
 void VP8DspInit(void) {
   DspInitTables();

third_party/libwebp/dsp/dsp.h

@@ -160,8 +160,10 @@ extern WebPUpsampleLinePairFunc WebPUpsamplers[/* MODE_LAST */];
 // Initializes SSE2 version of the fancy upsamplers.
 void WebPInitUpsamplersSSE2(void);
 
+#if defined(WEBP_USE_NEON)
 // NEON version
 void WebPInitUpsamplersNEON(void);
+#endif
 
 #endif    // FANCY_UPSAMPLING
 
@@ -204,7 +206,10 @@ extern void (*WebPApplyAlphaMultiply4444)(
 void WebPInitPremultiply(void);
 
 void WebPInitPremultiplySSE2(void);   // should not be called directly.
+
+#if defined(WEBP_USE_NEON)
 void WebPInitPremultiplyNEON(void);
+#endif
 
 //------------------------------------------------------------------------------
 

third_party/libwebp/dsp/enc.c

@@ -689,7 +689,9 @@ VP8QuantizeBlock VP8EncQuantizeBlock;
 VP8BlockCopy VP8Copy4x4;
 
 extern void VP8EncDspInitSSE2(void);
+#if defined(WEBP_USE_NEON)
 extern void VP8EncDspInitNEON(void);
+#endif
 
 void VP8EncDspInit(void) {
   InitTables();

third_party/libwebp/libwebp.gyp

@@ -66,7 +66,7 @@
     {
       'target_name': 'libwebp_dsp_neon',
       'conditions': [
-        ['target_arch == "arm" and arm_version >= 7', {
+        ['target_arch == "arm" and arm_version >= 7 and (arm_neon == 1 or arm_neon_optional == 1)', {
           'type': 'static_library',
           'include_dirs': ['.'],
           'sources': [