suppress warning during build using clang

[tomoaki0705]

I had a chance to build OpenCV with clang 10 and realized some warnings happening.
I created PR in OpenCV and now I'm porting to upstream.

/opencv/3rdparty/openjpeg/openjp2/j2k.c:7799:29: warning: implicit conversion from 'int' to 'float' changes value from 21
47483647 to 2147483648 [-Wimplicit-int-float-conversion]
            if (temp_size > INT_MAX) {
                          ~ ^~~~~~~
/usr/lib/llvm-10/lib/clang/10.0.0/include/limits.h:46:19: note: expanded from macro 'INT_MAX'
#define INT_MAX   __INT_MAX__
                  ^~~~~~~~~~~
<built-in>:37:21: note: expanded from here
#define __INT_MAX__ 2147483647
                    ^~~~~~~~~~
1 warning generated.

/opencv/3rdparty/openjpeg/openjp2/tcd.c:2265:35: warning: implicit conversion from 'int' to 'float' changes value from 21
47483647 to 2147483648 [-Wimplicit-int-float-conversion]
                    if (l_value > INT_MAX) {
                                ~ ^~~~~~~
/usr/lib/llvm-10/lib/clang/10.0.0/include/limits.h:46:19: note: expanded from macro 'INT_MAX'
#define INT_MAX   __INT_MAX__
                  ^~~~~~~~~~~
<built-in>:37:21: note: expanded from here
#define __INT_MAX__ 2147483647
                    ^~~~~~~~~~
1 warning generated.

It's just a warning of corner case, but I think it's worth preventing it.

[rouault]

thanks