more C89-fixes

going down to strict -ansi c89 is quite overkill (no 'inline',
and /* */-style comments).
But with these fixes, the code compiles with the stringent flags:
 -Wextra -Wold-style-definition -Wmissing-prototypes
 -Wmissing-declarations and -Wdeclaration-after-statement

Change-Id: I36222f8f505bcba3d9d1309ad98b5ccb04ec17e3

src/webp/decode.h

@@ -20,7 +20,7 @@ extern "C" {
 
 // Return the decoder's version number, packed in hexadecimal using 8bits for
 // each of major/minor/revision. E.g: v2.5.7 is 0x020507.
-int WebPGetDecoderVersion();
+int WebPGetDecoderVersion(void);
 
 // Retrieve basic header information: width, height.
 // This function will also validate the header and return 0 in
@@ -173,6 +173,8 @@ VP8StatusCode WebPIAppend(WebPIDecoder* const idec, const uint8_t* data,
 // A variant of the above function to be used when data buffer contains
 // partial data from the beginning. In this case data buffer is not copied
 // to the internal memory.
+// Note that the value of the 'data' pointer can change between calls to
+// WebPIUpdate, for instance when the data buffer is resized to fit larger data.
 VP8StatusCode WebPIUpdate(WebPIDecoder* const idec, const uint8_t* data,
                           uint32_t data_size);
 

src/webp/decode_vp8.h

@@ -83,13 +83,13 @@ struct VP8Io {
 };
 
 // Internal, version-checked, entry point
-extern int VP8InitIoInternal(VP8Io* const, int);
+int VP8InitIoInternal(VP8Io* const, int);
 
 // Main decoding object. This is an opaque structure.
 typedef struct VP8Decoder VP8Decoder;
 
 // Create a new decoder object.
-VP8Decoder* VP8New();
+VP8Decoder* VP8New(void);
 
 // Must be called to make sure 'io' is initialized properly.
 // Returns false in case of version mismatch. Upon such failure, no other

src/webp/encode.h

@@ -24,7 +24,7 @@ extern "C" {
 
 // Return the encoder's version number, packed in hexadecimal using 8bits for
 // each of major/minor/revision. E.g: v2.5.7 is 0x020507.
-int WebPGetEncoderVersion();
+int WebPGetEncoderVersion(void);
 
 //-----------------------------------------------------------------------------
 // One-stop-shop call! No questions asked: